The confinedness of undergrowth Picea obovata and Abies sibirica (Pinaceae) to tree-related microhabitats and their development features at various phases of post-fire succession in green-moss dark coniferous forests in the Northern Pre-Urals

Abstract

Forest ecology frequently explores the role of microsite mosaics in forest communities for the regeneration of forest-forming tree species. The present study aims to find out whether the ontogenetic structure and differentiation of Siberian spruce (Picea obovata) and Siberian fir (Abies sibirica) undergrowth plants by the plant vitality are associated with their occurrence on various microsites. The study has been carried out in the Pechora-Ilych State Nature Biosphere Reserve, Russia. In green-moss fir-spruce forests, 23 temporary sample plots were established, including 1) forest communities of the intermediate phase of post-fire succession (in areas where fires happened in 1850–1900) and 2) forest communities of the late phase (in areas where there were no fires, at least since the mid-XIX century). On the study plots, P. obovata and A. sibirica undergrowth individuals were recorded indicating ontogenetic state, vitality and microsite substrate for each plant. Using the Z-criterion, a comparison of the occurrence frequencies (%) of various undergrowth groups of P. obovata and A. sibirica on various microsites has been carried out, i.e. within each species and between the studied species, as well as at each phase of post-fire succession and between the phases. The analysis showed that, in communities of both succession phases in both species, undergrowth plants of ontogenetic state im2 occurred on deadwood logs less frequently than the undergrowth plants of the earlier ontogenetic state im1. At the same time, in both species on the flat ground surface an opposite occurrence trend for these ontogenetic states was revealed. In communities of the late succession phase, A. sibirica undergrowth plants of the ontogenetic state im2 and normal vitality occurred on a flat ground surface within inter-crown sites more frequently than plants of reduced and low vitality. A comparison between the species showed that in forest communities of both succession phases, A. sibirica undergrowth plants of im1 and im2 ontogenetic states more frequently occupy flat ground surface than deadwood logs, whereas P. obovata undergrowth plants more frequently grow on deadwood logs than on the flat ground surface. In addition, in communities of the intermediate succession phase, A. sibirica undergrowth is more likely than P. obovata to be found in the under-crown sites (especially on a flat ground surface). In communities of the late succession phase, A. sibirica undergrowth more often grows in under-crown sites on the near-trunk elevations of living trees. In both species, 40–50% of im2 plants of low vitality grow in inter-crown sites. To clarify the influence of the microsite mosaics on the regeneration processes in the studied forests, more detailed and large-scale studies are further needed, which will allow us obtaining more representative samples of undergrowth plants at various ontogenetic states.