Russians in the Siberian city of Irkutsk will face a smelly Christmas if they buy a stolen fir tree this year.
Disappearing firs worry Russia
"Operation Fir Tree" has been launched to protect the region's forests, reports the Ria Novosti news agency.
Siberia's chief tree specialist, Nina Markovahas, told the agency that the trees had been treated with a special anti-theft solution.
The chemical is odourless when cold but will emit an unbearable smell if the trees are placed in a warm room.
Siberian fir trees grow slowly - it can take up to 30 years for one to reach two metres.
Fifty police units, assisted by student environmental patrols, will be on duty round-the-clock over the holiday period to protect the city's fir trees from criminals.
Checkpoints have also been set up at access points to the city.
Anybody caught stealing a tree could face a year's public service and fines of $380.
Siberian fir trees are believed to have special medicinal qualities.
Rubbing the sap from a fir tree into a cut or graze is supposed to make it heal more quickly.