From pixels to pines: exploring Bulgaria’s Rhodopes Forests
#RestorationStory by Annabel Burg, Sietse van der Woude, and Niamh Kelly
It was the last day of June 2025 when our small group set out from Schiphol Airport. Traveling with us, three PhD students from Wageningen University and Research, were two colleagues: Gert-Jan Nabuurs, Professor of European Forest Resources at Wageningen University, and Thomas Groen, Associate Professor of Remote Sensing at the University of Twente. Our destination was Bulgaria – a country that, until then, most of us knew little about. We were curious, not only about its history and culture, but especially about its landscapes. Despite its modest size, Bulgaria is blessed with mountains, rivers, caves, and lakes. More than one-third of the country is covered by forests, making it one of Europe’s most densely forested and biodiverse nations.
The roots of this journey stretched back a few months earlier. In February, during a meeting in Suceava, Romania, Gert-Jan had spoken with Tzvetan Zlatanov, Professor of Ecosystem Research at the Bulgarian Academy of Sciences. That conversation marked the beginning of a collaboration. In the weeks that followed, Tzvetan shared with us a treasure trove of information: a forest inventory database compiled from over 150 forest enterprises across Bulgaria, with data on about one million forest stands. It was an extraordinary resource. But data can only take us so far. To truly understand forests, we also need to see them. And so, this trip was born – part scientific mission, part field validation, and part opportunity to experience Bulgarian forests firsthand.
Our scientific goals were clear. First, we wanted to deepen our understanding of the current state of Bulgarian forests and of the systems used to monitor and manage them. Second, we were eager to explore how new approaches – advanced modelling techniques and the integration of remote sensing – might complement and enhance existing forest information. In the months before our journey, Niamh had already analysed the database and produced a 100-year projection using the EFISCEN Space model. Meanwhile, Sietse applied the soon-to-be-published European Sentinel-1 radar-based RADD alerts to highlight recent disturbances in Bulgarian forests. These were powerful tools, but the next step was obvious: we needed to see the forests behind the numbers.
The trip was not only about science. It was also about people – about strengthening ties with Bulgarian colleagues, exchanging knowledge, and building the trust that makes collaboration possible. And, of course, it was about experiencing Bulgaria’s unique forests in person: from old-growth stands to the rare remnants of Europe’s untouched primary forests, which today cover just 0.5 percent of Bulgaria’s forest area.
When we arrived in Sofia, Tzvetan welcomed us warmly. Together, we continued our journey to Devin, a mountain town that would become our base for three days of exploration in the Rhodope region. Despite the long travel day, Tzvetan encouraged us to stretch our legs, and so we set off on a short hike. The path wound through a forest of cherry and hornbeam trees, leading us to the Samodivsko Praskalo waterfall. Standing there, with cool mist on our faces and the sound of rushing water in our ears, we had our first glimpse of the landscapes we had come to discover. The hike was brief – we were tired from the journey and knew that much lay ahead – but it offered a perfect introduction. The forests of Bulgaria were ready to reveal their stories.
Day 1: Walking barefoot on a floating bog
Our first day began with a one-hour drive to Trigrad, where we left our car at the Trigradsko gorge to hop on a 4×4 for an off-road ride towards a remote settlement near Chamla. Along the way, we passed through a highly diverse landscape of mainly black pine, Norway spruce, silver fir forests and dramatic rock formations. At the settlement, we were greeted by colleagues from Tzvetan’s institute, who were there to collect field data. Soon after, we were asked to take off our shoes to explore a nearby open peatland barefoot! The bog had slowly been flooded after the establishment of an embankment, until the vegetation detached from the bottom and started to float. In this rare floating habitat, black pines were slowly taking root, threatening the openness of the area. Using an increment borer, Tzvetan showed us that these trees, though small, were already around 50–60 years old. To ensure the peatland remained open, some of the trees had been girdled, which slowly kills them. After a delicious Bulgarian lunch of bean soup prepared for us by the owner of the “Chairski lakes” mountain hut, we continued on a hike through forest and meadows, spotting wildflowers and birds and taking in the mountain views. We returned to Devin already impressed by the landscapes we had seen, but our hosts assured us that even more incredible places awaited us in the days to come.
Photo: Old-growth black pine forests nestled on the steep cliffs.
Photo: Entering the bog: We let Gert-Jan cross the bog first to see if it would hold. You have to spend the old stuff first.
Day 2: Soskovcheto nature reserve and primary forests
On our second day, we headed further east to the Soskovcheto Nature Reserve, near the town of Smolyan. We found ourselves surrounded by numerous waterfalls, wooden bridges and steep hiking paths, all in the shadow of tall spruce trees. Petar, a local friend of Tzevtan’s who joined us on all the hikes, told us about the wildlife here, such as Western Caipercaillies and, of course, brown bears. One of the highlights was the Orpheus Waterfall, cascading an impressive 68 meters. Parts of the reserve can be described as untouched primary forest, recognisable by their towering old-growth trees and the abundant presence of standing and fallen deadwood – clear signs of natural forest dynamics. Gert-Jan, who has visited many old growth forests in Europe, said: “This is the most incredible primary forest I have ever seen in Europe.” Tzvetan explained that this relatively large area had been preserved for so long because the steep slopes and the river at the base kept it inaccessible. After this beautiful hike, we enjoyed another tasty Bulgarian lunch in Smolyan generously prepared by the local forest managers – and then it was time to get to work. A small symposium had been organized, where we presented our research to a group of local forest managers and researchers – and they shared theirs in return. Tzvetan gave an extensive overview of the work that had gone into collecting and analysing data for the designation of protected forest areas in Bulgaria. Niamh presented growing stock projections made using the Bulgarian forest inventory data, which sparked an interesting discussion on both the potential and the limitations of this data for modelling. Sietse’s work on forest disturbance detection piqued the interest of local forest managers, who recognised recent disturbances they had come across on the ground. They were also interested in how we can use such alerts to inform management decisions. Thomas presented an overview of recent work within ITC on forest species classification using high-resolution optical remote sensing, while Gert-Jan highlighted the importance of connecting detailed forest resource modelling with up-to-date forest industry data. Finally, the local forest management team gave us a historical overview of Bulgarian forest management and the impressive reforestation efforts. On our way back to Devin, we made a short stop in Shiroka Laka, a picturesque village known for its well-preserved traditional Rhodopean architecture.
Photo: Walking through the gorge in Soskovcheto Nature Reserve
Day 3: Climbing Orpheus Peak
Our legs were already feeling the hikes from the previous days, but there was no time to rest yet! On day three, we set out for another hike, this time near the village of Gela, a region that turns into a ski area in winter. With clear skies and temperatures around 30°C, it was hard to picture the slopes buried in snow during the colder months. Looking more closely, however, the forest showed damage from heavy, wet snow. Elsewhere too, we saw few signs of major recent forest disturbances: uneven-aged management is common across Bulgaria, while large fires and windthrows are relatively rare. Continuing along the trail, we enjoyed sweeping views over the Rhodopes, with alpine flowers in bloom, Eleonora’s falcons and honey buzzards overhead, and an impressive number of butterflies along the path. After a steady climb, we reached Orpheus Peak at 2,188 meters – the second-highest in the Rhodope Mountains – and paused to take in the panorama . From there, we descended nearly 900 meters back to Gela village, passing the remains of an early Christian basilica along the way (and really feeling it in our legs). We rounded off the day with a well-deserved drink at Petar’s home – the perfect way to end our final field day in the mountains.
Photo: Signs of large clearcuts made in the past in the distance, but otherwise extensive swaths of mature spruce.
Although we spend most of our time behind screens for our work, it is important to occasionally spend time outside like this, to connect with the forest we represent in numbers and pixels. To understand our data, the knowledge of local people is also invaluable. Besides enjoying the beautiful scenery, this trip deepened our understanding of the Rhodopean forests. It also strengthened our collaboration with the local experts who kindly took the time to show us around. That being said, in three days’ time we only saw a tiny corner of Bulgaria– and much still remains to explore on future hikes!
