Evidence of Evergreen Conifers Invasion into Larch Dominated Forests During Recent Decades

Abstract

Dark needle coniferous (DNC: Siberian pine, spruce, fir) expansion into larch dominated area was investigated along transects, oriented from the west and south borders of the larch dominated communities to its centre. The expected invasion of DNC into larch habitat was quantified as an increase of the proportion of those species both in the overstory and regeneration. Abundance and invasion potential was expressed using the following variables: (1) Ni and ni – the proportion of a given species in the overstory and regeneration, respectively, and (2) Ki – “the normalized propagation coefficient” defined as Ki = (ni − Ni)/(ni + Ni). The results show that Siberian pine and spruce have high Ki values both along the margin and in the centre of zones of absolute larch dominance, where their presence in the overstory is <1%. There is a tendency of Ki to increase for DNC and birch from south to north and from west to east. The age structure of the regeneration showed that it was formed mainly during the last 2–3 decades. Regeneration number correlates with winter temperature increase, showing winter temperatures importance for regeneration survive. The DNC invasion into larch habitat is wildfire dependant. Fires promote an invasion of DNC due to better ecological conditions on the burns. On the other hand observed climate-induced fire retune interval reduction may complicate DNC invasion into larch habitat, because larch regenerates better after fire than DNC since larger seed-trees amount. The results obtained indicate DNC and birch invasion into the larch habitat and its relation to the climatic changes for the last 3 decades. At the same time larch stand crown closure and larch invasion into tundra observed in the northern forest-tundra ecotone.