Patterns of epixylic vegetation on spruce logs in late-successional boreal forests

There is a wide diversity in composition and structure of epixylic vegetation that depends on the stage of overgrowing, species of logs, ecological conditions, geographical position and random factors. We analyzed vegetation on spruce logs in the late successional spruce forests of the Sphagnum-Myrtillus, Myrtillus and Oxalis types in northwestern Russia. Vascular plants, lichens, hepatics and mosses constitute, respectively, 18, 17, 21 and 44% of the flora on the decaying wood. The total number of species increases from the first to the second stage of overgrowing, and then decreases at the fourth stage. However, the number of species per plot barely changes. The dynamics of epixylic species and generalists depend on the phytosociological conditions. The described sequences of vegetation are divided into three types of microsuccession. The first type is characterized by the dominance of the epiphytes in the early stages and the epigeous species in the late stages. The low abundance of generalists and epixylics is observed in the spruce forests with well-developed ground feather moss cover. The second type of microsuccession has a small coverage and number of epigeous species and a significant share of generalists on the latter stages of overgrowing. It is connected with the herb-rich, mainly deciduous forests. The third type of microsuccession includes one more stage where one group of ground flora mosses (green mosses) is replaced with another one (Sphagnum). This is characteristic for the Sphagnum-Myrtillus type of spruce forests. (c) 2007 Elsevier B.V. All rights reserved.