Evaluation of larch trees (Larix Mill., Pinaceae)

Peter the Great Botanical Garden of the Komarov Boranical Institute has 148 larch samples (Larix Mill., Pinaceae) which represent 22 taxa. They are long-lived large trees, up to 200 years of age, representing the base for a forest stand of an arboretum and forming alleys in the oldest regular part of the Garden. The tallest trees reach 31,6 m (L. dahurica) and 113 cm in diameter (L. decidua and L. dahurica). Due to the warming in the St. Petersburg area, there is a noticeable drying found on the trees' crowns. Based on the results of an inventory in 2015, 43 trees can be assigned to the first category; the other 105 trees suffer from drying of shoots, twigs and branches. The degree of drying corresponds with the age of trees. One of the possible reasons of the deterioration in the conditions of larch trees at the arboretum of the Komarov Botanical Institute may be the influence of the Phytophthora species. Soil research samples show presence of Phytophthora syringae (Berk.) Kleb. in the risosphere of L. decidua. It is the first time, this species of Phytophthora has been discovered at the Peter the Great Botanical Garden.