Long-Term Dynamics of Mixed Fir-Aspen Forests in West Sayan (Altai-Sayan Ecoregion)

Abstract

Space-temporal dynamics of secondary mixed fir-aspen forest types is considered by the example of the communities typical of chern forest zone (Abies sibirica – Populus tremula + Athyrium filix-femina – Matteuccia struthiopteris – Anemone baicalensis) in perhumid and moderate-continental climate of the Altai-Sayan Ecoregion (South Siberia). Different variants of 40-year-long succession typical of one native forest type are described on permanent plots: (1) Aspen forest with large ferns and herbs. (2) Fir-aspen forest with less developed floor of the same species, which is transformed rapidly into mixed forest with dominance of fir and a poorly developed layer of boreal and nemoral herbs. (3) Siberian pine stand with well developed herbaceous layer. The last variant was formed with the help of cleaning cutting; species diversity and composition remain similar to Aspen forest. The comprehensive data on dynamics of the communities’ structure are presented. To estimate the rate of successions in the secondary fir-aspen forests qualitative and quantitative methods were applied. Index of succession rate, Sorenson’s dissimilarity coefficient and the Shannon index of species diversity were used. The study highlights the importance of spatial heterogeneity, especially within herb layer, for the regeneration and long-term coexistence of Fir, Aspen and Siberian pine. Dense herb layer of tall forbs and ferns form the main barrier to Siberian pine regeneration and further immature stages even more than shade-tolerant Fir bio-groups. The permanent plots allow us to research all the transformations in space pattern and to learn intra- and inter-specific relationships and trends of succession in chern tall-forbs mixed forests.