Transformation of ground vegetation under the effect of fires in pine forests of Middle Siberia

Abstract

In Siberia, pine forests are widespread and grow in diverse habitats. Under zonal conditions, pine shows a wide amplitude of ecological flexibility, being an edificator species in areas with different soils, from shallow podzols with a low base exchange capacity to soddy calcareous soils. The expansion of pine forests far beyond the limits of the zone with a true forest (boreal) climate is apparently explained by the ability of pine to take full advantage of local edaphic conditions, thereby alleviating the impact of adverse climatic factors and broadening its potential climatic range. In this respect, pine is superior to other conifers (Shumilova, 1962). The range of pine forests in Siberia is mainly confined to the Angara basin in its upper and lower reaches and to the watershed separating it from the upper reaches of the Podkamennaya Tunguska, Lena, and Nizhnyaya Tunguska rivers. These forests are typologically diverse, but forest types with green mosses, lichens, and mesoxerophytic herbs dominating in the ground vegetation are more widespread. Fires in boreal forests are a permanent natural factor accounting for the formation of their structure and species diversity. In pine forests, they have always been a factor of evolutionary significance, since these forests are characterized by a high fire frequency. The vegetation of pine forests had been exposed to selection by fires for many millennia, which provided for the development of a variety of adaptations to the impact of fires in pine and produced a significant effect on the composition and properties of its ecobiomorphs, species, and biotypes (Sannikov, 1973). The frequency of fires in pine forests depends on their zonal location and the degree of landscape isolation. In pine forests of Central Siberia, the average interval between fires was estimated at 38.5 years (McRae et al., 2006). A relatively simple structure, ecological flexibility, and high fire frequency in pine forests make them a convenient object for studying the dynamics of postfire succession. The purpose of this study was to reveal changes in the species diversity and structure of ground vegetation at early stages of pyrogenic succession after fires of different intensities. Studies were performed in a dwarf shrub‐lichen‐ green moss pine forest growing on an island in a bog located on the right bank of the Togulan River, which flows into the Yenisei in its middle reaches. This forest occupies a low ridge with a depression in the middle, at an elevation of 60 m a.s.l. The uneven-aged pine stand (10P) is of quality classes 4 and 5, with tree diameter and height averaging 26 cm and 22 m. The undergrowth (10P) is also uneven-aged, up to 0.5 m high; its distribution is uniform. The shrub layer is sparse and consists of Rosa acicularis and Salix caprea . Ground vegetation is differentiated according to microenvironmental conditions. The moss layer is dominated by Pleurozium schreberi , with its coverage ranging from 60 to 100%. In the lichen layer (20‐100% coverage), Cladina arbuscula, Cl. rangiferina, and Cl. stellaris are dominant. The herb‐dwarf shrub layer is 20‐35 cm high, and its coverage varies from 15‐20% to 40%. Dominance belongs to mesophytic dwarf shrubs. The main dominants are Vaccinium vitis-idaea in relatively welldrained biotopes, Vaccinium myrtillis in mesotrophic biotopes, and Ledum palustre and Vaccinium uliginosum in overmoistened sites.