Evidence of evergreen conifer invasion into larch dominated forests during recent decades in Central Siberia [Russian Federation]
Models of climate warming predict the migration of 'warm-adapted' species to habitats of 'cold-adapted' species. Here we show evidence of the expansion of 'dark-needle' conifers (DNC: Siberian pine, spruce and fir) into the habitat of larch, the leader in adaptation to harsh climatic conditions in Asia. The studies were made along two transects oriented from the western and southern borders of a larch dominated forest to its center. The invasion of DNC into the historical larch habitat was quantified as an increase of the proportion of those species both in the overstory and in regeneration. Abundance and invasion potential were expressed using the following variables: (1) Nsub(i) and nsub(i), the proportion of a given species in the overstory and in regeneration, respectively, and (2) Ksub(i), the normalized propagation coefficient' defined as Ksub(i)=(nsub(i)-Nsub(i))/(nsub(i)+Nsub(i)). The results show that Siberian pine and spruce have high Ksub(i) values both along the margins and in the center of zones of absolute larch dominance even where their presence in the overstory is 1%. There is a tendency for Ksub(i) to increase for DNC and birch from south to north and from west to east. The age structure of regeneration showed that regeneration occurred mainly during the last 2-3 decades. In particular, warm winter temperatures promote the survival of regenerated Siberian pine. The results obtained indicate the climate-driven migration of Siberian pine, spruce and fir into traditional zone of larch dominance. Substitution of a deciduous conifer (larch) by evergreen conifers decreases the albedo and may provide positive feedback for temperature increases.