| Summary: | Old-growth spruce and spruce-fir forests can be extremely variable in the composition and diversity
of their ground layer of vegetation, sometimes with over 10 times difference in diversity between various forests.
What is the reason for such a big difference? Here we propose a hypothesis that the ground layer of vegetation is
most strongly affected by fire history of boreal forest ecosystems. We estimated composition, structure and diversity
of vascular plant and bryophyte species in seven forest types in old-growth forests dominated by either
Picea obovate or Picea obovate together with Abies sibirica, which were located in the plains of the Komi Republic.
All the study areas were either at elevated or hilly plains with good and moderate drainage, or in valleys of small
rivers and streams, away from wets and bogs. We analyzed Landolt’s species ecological values, coverage of vegetation
layers and deadwoods at different stages of decay, bedrock parameters, and soil charcoals in order to explain
differences in the plant species composition and diversity. We showed that there are weak but statistically
significant correlations between the coverage of deadwoods at different decay stages and vascular species composition
and a positive correlation between the total deadwood coverage and bryophyte species diversity. Among
the studied forests, those that are dominated by boreal and nitrophilous tall herbs (located in watersheds and in
river valleys respectively), have no fire scars on stems of Pinus spp. and almost no charcoal in the soil and demonstrate
the highest species diversity. We estimated that these forests have not experienced fires for over 400 years.
In contrast, the diversity of vascular plants in the forests dominated by green mosses, dwarf shrubs, small boreal
herbs and large ferns was low; we evaluated that the last time when these forests suffered intense multiple fires
was at least 150 years ago.
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