Ecology of Tilia sibirica in a continental hemiboreal forest,southern Siberia: An analogue of a glacial refugium of broad-leaved temperate trees?

Abstract

Siberian lime (Tilia sibirica) is a broad-leaved deciduous tree closely related to European Tilia cordata. It is endemic to a few sites in southern Siberia, located approximately 2000 km east of the limit of the European deciduous forest biome. These isolated sites with locally increased precipitation can be considered as potential analogues of the glacial refugia of temperate trees. To understand the ecology of such refugia, we studied the history and recent dynamics of the forests containing T. sibirica using soil charcoal and tree-ring analyses at the largest locality of this species (Kuzedeevo). These forests are currently dominated by Populus tremula and Betula pendula, with scattered occurrence of Abies sibirica and Tilia, which form small monodominant stands locally. Soil charcoal indicated continuous occurrence of all of these trees more than 1000 years ago, but the dominant species in the past were Abies and Populus. Current patches of Tilia-dominated forests are even-aged, 40–80 years old, with tree-ring patterns indicating their origin in open areas, probably after logging in the 20th century. After disturbance, Abies seedlings tend to be outcompeted by tall herbs, whereas Tilia can form small monodominant stands through vegetative regeneration. However, in the natural undisturbed Abies–Populus forest, Tilia was probably a subordinate species. Analogously to this modern Siberian ecosystem, temperate deciduous trees, especially those with vegetative regeneration, may have survived as rare components of coniferous forests in glacial periods at locally favorable sites such as those with increased orographic precipitation and protection by a thick snow cover.