Hidden Ecological Cost of War Fires Emerging Across Eastern Ukraine’s Fragile Pine Forests

Military fires are reshaping forests in eastern Ukraine in ways that may continue years after the fighting ends. A study titled 'War fires promote short-term alien plant colonization in eastern Ukraine's pine forests,' published in the nature journal Scientific Reports, examined how fires linked to Russia's full-scale invasion affected plant life and tree recovery near Izium in the Kharkiv region.

Researchers Maksym Matsala, Roman Zadorozhniuk, Olena Miskova, Heorhii Bondarenko and Andrii Bilous found that severe fire damage created favourable conditions for non-native plants, natural tree regeneration remained weak, and overall plant diversity showed no clear response to burn severity.

Drones entered forests that researchers could not safely walk through

The forests around Izium contain large areas of Scots pine planted during the twentieth century on dry, sandy and nutrient-poor soils where sparse woodlands and grasslands once dominated. These uniform plantations were already vulnerable to drought and wildfire before the invasion; now shelling, repeated ignitions, landmines, unexploded weapons and disrupted forest management have created a far more dangerous disturbance pattern.

Researchers surveyed 29 pine-dominated stands in September 2025, three years after military activity and fires affected the area in 2022. The selected locations had burned only once during that period and were about 50 kilometres from the active frontline, allowing the team to work from relatively safe forest roads and firebreaks.

A DJI Phantom 4 Pro drone was flown manually beneath the tree canopy at a height of roughly one to two metres, capturing downward-facing photographs of ground vegetation along transects measuring between 90 and 360 metres. This approach allowed the scientists to examine plants and young trees without walking across potentially mined ground. Two researchers identified species and estimated their cover from the images, then cross-checked their results.

The team used satellite-based burn measurements, visible scorch marks on tree trunks and estimated burned-patch sizes to assess fire severity. Forest age, tree density, soil fertility, site productivity and distance from firebreaks were also considered. A resampling process standardized comparisons between transects that contained different numbers of photographs.

Severe burns opened the door to alien plants

Alien species accounted for about 23% of the ground vegetation recorded across the studied forests. Canadian horseweed was the most common non-native plant, joined in smaller amounts by prickly lettuce, common sowthistle and downy brome, all species that can quickly occupy disturbed and exposed ground.

Fire severity was significantly connected to a declining proportion of native vegetation, meaning that more heavily damaged sites contained a larger share of alien plants. This relationship remained strong after the researchers accounted for the spatial grouping of the forest stands, supporting their first hypothesis that increasing war-related damage encourages non-native flora during early recovery.

Canadian horseweed commonly spreads across burned or disturbed land and is often replaced by meadow and forest species within three or four years. Repeated fires linked to warfare could interrupt that natural turnover, keeping alien and disturbance-loving plants in the landscape for much longer, possibly for up to a decade.

Dense seasonal growth may also produce fine, dry fuel that connects damaged forest patches with surrounding grasslands and surviving tree stands. Eastern Ukraine's moisture shortages can make this vegetation especially flammable during early spring. Shelling can ignite fires even when weather conditions would not normally support a major wildfire, creating patchy burns that leave mature trees standing around newly opened areas while repeatedly disturbing the ground below.

Young trees remain scarce despite newly opened space

The researchers expected severe burns to encourage tree regeneration because damaged canopies allow more sunlight to reach the forest floor, and the loss of dense ground vegetation can reduce competition for water, nutrients and space. The results did not support that expectation:

An estimated 88.4% of surveyed photographs contained no young trees: Average regeneration density was calculated at 681 individuals per hectare, and the median was only 212 per hectare because a small number of densely regenerating patches pushed the average upward. Some photographs contained clusters of aspen, oak or birch growing through vegetative shoots, meaning high local counts did not represent recovery across the wider forest.

Eleven woody species were identified on 24 transects: Common aspen was found most frequently, appearing on 15 transects with regeneration, followed by common oak on nine. Scots pine appeared on only four transects and was represented by just nine young trees. Birch, hybrid poplar, wild pear, black locust and wych elm were recorded at two locations each, while Tatar maple, black poplar and willow appeared only once.

Stand age was the only factor with a positive connection to the number of new trees. Older stands may offer more mature seed-producing trees around the edges of patchy burns, while large dead trunks can create sheltered microsites where seedlings have a better chance of surviving. Low rainfall and dry soil may still outweigh these benefits, explaining why recovery was much weaker than patterns reported from wetter pine forests in northern Ukraine and the Chornobyl Exclusion Zone.

Fire severity alone does not explain the forest's future

The team recorded generally low plant diversity, with an average Shannon diversity score of 0.94 and a median of seven vascular plant species per transect. Forest-associated plants, grassland species, plants adapted to sandy soils and disturbance-loving weeds all occurred within the survey area.

Burn severity had no significant effect on the number of vascular plant species, their overall diversity or how evenly they were distributed, leaving the researchers' third hypothesis unsupported. Water availability may place a stronger limit on plant communities than canopy damage in these consistently dry forests.

Site productivity was associated with fewer recorded plant species but greater evenness, a pattern that cannot be explained by soil fertility alone because the direct fertility measure was not significant. Distance from firebreaks, remaining tree density and fertility class also failed to predict any of the main outcomes.

The findings describe only one early stage of recovery in dry, managed pine monocultures. The research did not cover wetter alder forests, oak plantations, naturally occurring pine woodlands, forests repeatedly burned since 2022 or the region's rare chalk-pine ecosystems. Some of these habitats are inaccessible because of mines, while dense canopies make their understory vegetation difficult to observe remotely.

Mines could prevent grazing, firefighting, fuel removal and forest restoration for many years, allowing dry vegetation to accumulate behind fenced-off areas. Frequent reburning could keep alien plants established, block tree regeneration and push artificial pine forests towards open grassland, deforestation or desertification. The study shows that drones can provide valuable ecological evidence in dangerous landscapes, while its results warn that ending the fighting will not automatically end the environmental damage.