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Aim of study: We aim at (i) developing a reference definition of mixed forests in order to harmonize comparative research in mixed forests and (ii) review the research perspectives in mixed forests.Area of study: The definition is developed in Europe but can be tested worldwide.Material and Methods: Review of existent definitions of mixed forests based and literature review encompassing dynamics, management and economic valuation of mixed forests.Main results: A mixed forest is defined as a forest unit, excluding linear formations, where at least two tree species coexist at any developmental stage, sharing common resources (light, water, and/or soil nutrients). The presence of each of the component species is normally quantified as a proportion of the number of stems or of basal area, although volume, biomass or canopy cover as well as proportions by occupied stand area may be used for specific objectives. A variety of structures and patterns of mixtures can occur, and the interactions between the component species and their relative proportions may change over time.The research perspectives identified are (i) species interactions and responses to hazards, (ii) the concept of maximum density in mixed forests, (iii) conversion of monocultures to mixed-species forest and (iv) economic valuation of ecosystem services provided by mixed forests.Research highlights: The definition is considered a high-level one which encompasses previous attempts to define mixed forests. Current fields of research indicate that gradient studies, experimental design approaches, and model simulations are key topics providing new research opportunities.Keywords: COST Action; EuMIXFOR; mixed-species forests; admixtures of species.

Abstract. The relative role of fire and of climate in determining canopy species composition and aboveground carbon stocks were investigated. Measurements were made along a transect extending from the dark taiga zone of central Siberia, where Picea and Abies dominate the canopy, into the Larix zone of eastern Siberia. We test the hypotheses that the change in canopy species composition is based (1) on climate-driven performance only, (2) on fire only, or (3) on fire-performance interactions. We show that the evergreen conifers Picea obovata and Abies sibirica are the natural late-successional species both in central and eastern Siberia, provided there has been no fire for an extended period of time. There are no changes in performance of the observed species along the transect. Fire appears to be the main factor explaining the dominance of Larix and of soil carbon. Of lesser influence were longitude as a proxy for climate, local hydrology and active-layer thickness. We can only partially explain fire return frequency, which is not only related to climate and land cover, but also to human behavior.Stand-replacing fires decreased from 300 to 50 yrs between the Yenisei Ridge and the upper Tunguska. Repeated non-stand-replacing surface fires eliminated the regeneration of Abies and Picea. With every 100 yrs since the last fire, the percentage of Larix decreased by 20 %.Biomass of stems of single trees did not show signs of age-related decline. Relative diameter increment was 0.41 ± 0.20 % at breast height and stem volume increased linearly over time with a rate of about 0.36 t C ha −1 yr −1 independent of age class and species. Stand biomass reached about 130 t C ha −1 (equivalent to about 520 m 3 ha −1 ). Individual trees of Larix were older than 600 yrs. The maximum age and biomass seemed to be limited by fungal rot of heart wood. 60 % of old Larix and Picea and 30 % of Pinus sibirica trees were affected by stem rot. Implications for the future role of fire and of plant diseases are discussed.

International audienceForest management and disturbances affect forest soils and biomass carbon stocks, emissions to the atmosphere, and radiative forcing. The conventional approaches to quantifying the intensity of land management based on net primary productivity (NPP) are limited because they lack a sound ecological basis. These limitations are especially evident for forests. This study proposes a new way of characterizing the degree of management and disturbance in forest stands that do not experience a change in classification, i.e., they remain forests. The proposed index, called land use and disturbance intensity (LUDI), uses the relationship between stand density and diameter at breast height for a relatively unmanaged/pristine baseline forest and different management schemes, in conjunction with the self-thinning relationship, to calculate the difference between potential and actual biomass storage. The LUDI distinguishes between the long and short timescales associated with management and disturbance. This capacity sets it apart from the conventional NPP-based approaches currently used to quantify the disturbance intensity. The study uses a semi-qualitative validation approach to demonstrate that the proposed index reproduces textbook knowledge on management and disturbance intensity. However, our quantitative approach that distinguishes between timescales adds insight into the effects of forest management on the living biomass stock. Further, data from the German national forest inventory were used to demonstrate that the proposed index does not require knowledge about the management scheme. Although LUDI is constrained to aboveground living biomass, we believe that the approach is useful in the context of broadening our capability in large-scale management reconstruction and through this understanding the effects of land use on the carbon cycle, beyond effects of deforestation and afforestation