Impact of litter burning on alpine <i>Festuca varia</i> grasslands of the Northwestern Caucasus

Abstract

Fires play an important role in structure and function of terrestrial ecosystems, but their long-term impact on the composition and structure of plant communities in humid high mountain regions remains almost not studied. At the most dry alpine grasslands, dominated by a dense-tussock grass Festuca varia, with substantial accumulation of non-decomposed litter, the 23-years long experiment with regular (every two years) litter burning was established. The composition of plant community changed significantly. The mortmass (mass of litter), aboveground vascular plant biomass and relative abundance of dominants decreased substantially. In aboveground biomass the proportion of grasses decreased and that of forbs increased. The shoot numbers of Anthemis cretica, Campanula collina, Deschampsia flexuosa, Festuca ovina, Nardus stricta, and Veronica gentianoides increased after burning. Two-fold increase of alpha-diversity of vascular plants was observed on plots with burning treatment, it was twice as high as initial value, and was significantly higher than the values in the control plots. Long-term burning did not substantially change mean P, Ca and Mg content in the biomass of the most of studied species, only K content decreased in some species, while Mg content increased in Festuca varia and Nardus stricta. The increase of P and Mg content in the mortmass was observed. During long-term burning, weak soil acidification and the decrease of Ca content, as well as strong decrease of nitrogen content and the intensity of nitrogen transformation processes were observed. Generally, the observed patterns were similar to those in other studied herb communities, however, the decrease of K content during the regular burning was not reported earlier.