Ladoga Skerries is a national park on the NW coast of Lake Ladoga. Its landscape is unique, with no analogs elsewhere in Russia. The park features high biodiversity and significant recreational potential. In 2024 and 2025, researchers from the KarRC RAS conducted comprehensive expeditions aboard the Poseidon research vessel, covering a group of islands including Tulolansaari, Myakisalo, Pelotsaari, Karpansaari, Laponsaari, Kirkkosaari, Raipatsaari, Suri-Sartosaari, Orjatsaari, and Pieni-Sartosaari. During the surveys, data were collected to assess the current state and detect changes in the land cover through comparisons with satellite imagery. The research team includes Nikolai Petrov, Boris Raevsky, and Viktor Tarasenko of the KarRC RAS Department for Multidisciplinary Research.
Boris Raevsky, Leading Researcher at the Ecological Monitoring and Modeling Laboratory DMR KarRC RAS, takes measurements of an old spruce tree
– This work is of both applied and theoretical value. The applied perspectives have to do with environmental management optimization in the national park, first of all by updating information on the current state of the land cover. The available data on the forest fund in the area are significantly outdated. To conserve valuable ecosystems, it is essential to understand their current condition, as well as how and why they change over time. We also need to study the resilience of vegetation in insular ecosystems, as they are the most vulnerable to anthropogenic impact and climate change, – explained Nikolai Petrov, Researcher at the Ecological Monitoring and Modeling Laboratory DMR KarRC RAS.
Seeking to comprehend the patterns of land cover change, specialists constructed digital elevation models by interpreting satellite images taken at different times by the Sentinel and Landsat programs. Remote sensing data treatment was facilitated by the Google Earth Engine (GEE) cloud computing platform. It provides access to satellite imagery and various computational algorithms.
Multispectral satellite images were interpreted using supervised classification algorithms based on machine learning. The accuracy of the resulting geospatial models was assessed through standard mathematical procedures and with reference to in situ vegetation descriptions. During the expeditions, the researchers established over 40 sample plots in the most typical forest sites. Within these plots, a complete tree census was conducted, with documentation of diameter, height, and age. At each control point, a geobotanical description of the ground cover was made, and a soil pit exposing the profile was dug.
Nikolai Petrov and Boris Raevsky in the field, documenting vegetation in the Ladoga Skerries
The results of decoding Tulolansaari archipelago images from different times are presented as a set of digital maps. Having analyzed them, the scientists determined that most of the archipelago's land is forest-covered (93%). Coniferous stands prevail (46.9%), mainly represented by pine forests. The area of meadow communities is shrinking, getting overgrown with woody and shrubby vegetation, which ultimately leads to an increase in the area of deciduous stands.
– It is noteworthy that the land cover in the Northern Ladoga region has been widely altered anthropogenically for many centuries. At the turn of the 19th and 20th centuries, this was a land of highly developed smallholder farming and mining. Until the 1940s, forests were being logged intensively, and all land suitable for cultivation was plowed up, – noted Nikolai Petrov.
Since the second half of the 20th century, forests throughout the Northern Ladoga area have been assigned to various protection categories, so clear-cutting was not practiced there. In the 1990s, subsidiary farms of large industrial enterprises ceased to exist. The study has confirmed the scientists' expectations: given the historical realities, the area of coniferous stands has remained virtually unchanged in recent decades, while abandoned farmlands are getting actively overgrown with woody and shrubby vegetation.
Rowan stand, at least 80 years old, growing where a hamlet used to be
Field surveys also showed that significant areas of rupicolous pine forest have been affected by surface fires. After a fire, large trees in such habitats gradually fall down over the first two to three years, and a natural regenerative succession involving Scots pine begins.
The researchers created digital vector layers of probable fire events on the archipelago’s islands. Having processed the computation output, they identified the time periods with the greatest total area of vegetation loss. These were mainly the warm seasons between 1994 and 2007.
“The actual burnt areas are predominantly located on medium-sized rocky islands, which typically fringe the skerry zone, i.e. in the most recreationally attractive places. Usually starting from the shoreline, the fire spreads up the pine-overgrown rocky slope, sometimes reaching further spruce stands”, – remarked the authors of the article published in the Transactions of KarRC RAS.
All in all, surface fires, likely associated with human impact, have affected around a third of the total lichen-type pine forest area in the archipelago.
Thematic maps: À – “coniferous stands” inferred from 1987 Landsat-5 imagery; B – probable fires of 1987–2024, broken down by detection times. Images from Transactions of KarRC RAS
The scientists concluded that the study of the land use and land cover structure of the Tulolansaari Archipelago has revealed its main patterns and the characteristics of its anthropogenic and natural dynamics. Modern methods have significantly reduced the time for computerized processing of large datasets, providing high accuracy and reliability of satellite imagery classification.
The methodological approaches developed during the study can serve as a foundation for creating a modern set of tools for timely monitoring of the vegetation cover in Karelia as well as other regions of Russia. Specialists at the KarRC RAS Department for Multidisciplinary Research plan to expand their work in the Ladoga Skerries towards the Leningrad Region and gradually cover the entire national park.
Photos provided by the researchers