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Tree species influence the litter decomposition process by influencing litter quality and soil microclimate. Furthermore, over the long term, trees could promote soil communities that are particularly capable of degrading the litter they encounter most often. Thus, plant litter could decompose faster when placed in the habitat from which it was derived than in a foreign habitat, which has been termed home field advantage (HFA) of litter decomposition. In mixed-plant species environments however, it is not known whether a specific decomposer community under one tree species is affected by the presence of another tree species in the vicinity. To address this question, we tested if spruce and poplar litters showed HFA in mono-specific and in mixed species plantations under each tree species by reciprocally transplanting litter in the two plantation types. Decomposition rates, as well as the composition and ability of decomposer communities to degrade the different types of litter, were monitored during two years. Only spruce litter exhibited a faster decomposition rate at home. This HFA could be explained by higher abundance of decomposers. Furthermore, cellulose and poplar litter decomposed less or similarly in spruce plantations, suggesting that soil communities of that environment were capable of specifically degrading spruce litter. In mixed plantations, HFA was in the same direction as in mono-specific plantations, but was not as strong, indicating that HFA is sensitive to the surrounding plant community. Furthermore, this 'mixed environment' had synergistic effects on decomposition rates under poplar trees. These 'tree environment-specific' results highlighted the possible importance of spatial distribution of each litter on decomposition rates in mixed stands. Thus, the influence of litter dispersal should be taken into account in future studies. [ABSTRACT FROM AUTHOR]

Fire, which is the dominant disturbance in the boreal forest, creates substantial heterogeneity in soil burn severity at patch and landscape scales. We present results from five field experiments in Yukon Territory, Canada, and Alaska, USA that document the effects of soil burn severity on the germination and establishment of four common boreal trees: Picea glauca, Picea mariana, Pinus contorta subsp. latifolia, and Populus tremuloides. Burn severity had strong positive effects on seed germination and net seedling establishment after 3 years. Growth of transplanted seedlings was also significantly higher on severely burned soils. Our data and a synthesis of the literature indicated a consistent, steep decline in conifer establishment on organic soils at depths greater than 2.5 cm. A meta-analysis of seedling responses found no difference in the magnitude of severity effects on germination versus net establishment. There were, however, significant differences in establishment but not germination responses among deciduous trees, spruce, and pine, suggesting that small-seeded species experience greater mortality on lightly burned, organic soils than large-seeded species. Together, our analyses indicate that variations in burn severity can influence multiple aspects of forest stand structure, by affecting the density and composition of tree seedlings that establish after fire. These effects are predicted to be most important in moderately-drained forest stands, where a high potential variability in soil burn severity is coupled with strong severity effects on tree recruitment. [ABSTRACT FROM AUTHOR]