Mysterious leaf loss affects birch trees across southern Finland

A wave of reports has emerged this year about birch trees shedding leaves prematurely, particularly along roadsides, tree-lined paths, and other open areas in southern Finland, according to the Natural Resources Institute Finland (Luke).

Observations have been concentrated in Southwest Finland, but similar cases have also appeared in the Helsinki region, Kanta-Häme, and Pirkanmaa. While the phenomenon is locally striking, most birch trees in the landscape remain healthy.

The exact cause of the leaf loss is still unknown, Luke’s leading researcher Tiina Ylioja said in a statement. The widespread nature suggests environmental stress factors—such as drought, temperature fluctuations, road salt, or soil compaction—may be contributing, either individually or in combination.

In some trees, buds have failed to open normally, leaves have not formed, and parts of last year’s shoots have died. Unlike previous years in Lahti, where birch trees suffered from the fungal “hat disease” (birch rust leaf spot), the current issue is not linked to fungal infection.

Luke is investigating the cause, with samples taken from branches to identify potential fungal species. More detailed results are expected in autumn.

Ylioja noted that leaf loss does not necessarily mean the tree is dying. If the root system is healthy and sufficient foliage remains, the birch may recover and produce new shoots later in the growing season.

No specific control measures are currently available. The situation should be monitored through the summer, and any trees showing severe or rapidly worsening symptoms should be reported as forest damage observations.