Revealing the ecological consequences of bark multifunctionality and its underlying traits has become a relatively new but essential focus in plant ecology. Although the enormous differences between the most crucial bark layers, i.e., inner and outer bark, in structure and functions have been widely recognized, the overall bark has been regarded as a homogenous tissue in most bark-related studies. This has led to poor knowledge on the functional independence, specialized contributions and possible linkages of inner and outer bark traits across tree species when further evaluating the crucial ecosystem functions that bark provides, especially in driving variation in bark decomposition. To fill this research gap, we used a “common garden experiment” on deadwood of six gymnosperms in a temperate forest in the Netherlands over four years of decomposition. We evaluated the differences and associations between inner and outer bark in initial functional traits, decomposition rates and afterlife effects of traits in driving in-situ bark decomposition across tree species at the earlier decomposition stage. We report four main findings: 1) inner and outer bark traits varied significantly and were not coordinated across tree species; 2) correspondingly, the decomposition of inner and outer bark were asynchronous and not coordinated across species and inner bark generally decomposed faster than outer bark; 3) the strong predictive traits driving bark decomposability were bark layer-specific, with several inner bark traits controlling inner bark decomposition rates but outer bark decomposability being poorly predicted by outer bark traits; 4) besides being controlled by inner bark traits, inner bark decomposition was also indirectly regulated by several functional traits and the structure-related trait spectrum of outer bark. Synthesis. This is the first study that has linked functional traits, decomposability and afterlife effects of inner and outer bark within the bark quantitatively. We highlight the significance of separating functional traits and ecological consequences of inner and outer bark in research in bark ecology and deadwood dynamics, rather than erroneously considering bark as a homogeneous tissue. Such research will help to better evaluate the function-oriented contribution of bark to the turnover of forest carbon and biogeochemical cycles from local to global scale.

1. Subordinates have relatively low abundance compared to dominants, but they may contribute substantially to functional diversity and ecosystem functions, especially if they differ strongly from the dominants in key traits. Here we investigated whether this phenomenon can be applied to litter decomposition as a key carbon and nutrient cycling process. 2. We hypothesized that species’ litter mass-weighted predictions of community-level litter decomposition based on the rates of dominants only would deviate strongly from observed community-level rates and that predictions would improve as subordinates with strongly contrasting traits were combined with those of the dominants. 3. We tested this hypothesis through a one-year field decomposition experiment across a chronological sequence in subtropical evergreen broad-leaved forest. The experiment included single-species litter of evergreen dominants, evergreen subordinates, deciduous subordinates, respectively, as well as community-level litter mixtures. 4. The expected community weighted mean decomposition rates based on the evergreen dominants alone, with or without the addition of evergreen subordinates, deviated strongly from those of observed community litter mixture at the middle and late succession stages but not at the early stage. When adding the deciduous subordinates to the expectation, there was no longer any difference to observed community litter decomposition rate across succession stages. Deciduous subordinates alone explained 7%, 21% and 15% of the total variation in community litter mixture decomposition rate for early, middle and late successional stage, respectively, i.e., more than would be expected from their litter mass fraction. 5. Synthesis. Deciduous subordinates with strongly contrasting nutritional and water-storing traits compared to the dominant evergreens significantly impact litter decomposition at the community-level in spite of their low abundance. This study highlights the importance of “being different” for subordinates to be influential in ecosystem carbon cycling.

Our basic understanding of plant litter decomposition informs the assumptions underlying widely applied soil biogeochemical models, including those embedded in Earth system models. Confidence in projected carbon cycle-climate feedbacks therefore depends on accurate knowledge about the controls regulating the rate at which plant biomass is decomposed into products such as CO2. Here, we test underlying assumptions of the dominant conceptual model of litter decomposition. The model posits that a primary control on the rate of decomposition at regional to global scales is climate (temperature and moisture), with the controlling effects of decomposers negligible at such broad spatial scales. Using a regional-scale litter decomposition experiment at six sites spanning from northern Sweden to southern France – and capturing both within and among site variation in putative controls – we find that contrary to predictions from the hierarchical model, decomposer (microbial) biomass strongly regulates decomposition at regional scales. Further, the size of the microbial biomass dictates the absolute change in decomposition rates with changing climate variables. Our findings suggest the need for revision of the hierarchical model, with decomposers acting as both local- and broad-scale controls on litter decomposition rates, necessitating their explicit consideration in global biogeochemical models.

Fire behavior of plant mixtures includes a complex set of processes for which the interactive contributions of its drivers, such as plant identity and moisture, have not yet been unraveled fully. Plant flammability parameters of species mixtures can show substantial deviations of fire properties from those expected based on the component species when burnt alone; that is, there are nonadditive mixture effects. Here, we investigated how fuel moisture content affects nonadditive effects in fire behavior. We hypothesized that both the magnitude and variance of nonadditivity in flammability parameters are greater in moist than in dry fuel beds. We conducted a series of experimental burns in monocultures and 2‐species mixtures with two ericaceous dwarf shrubs and two bryophyte species from temperate fire‐prone heathlands. For a set of fire behavior parameters, we found that magnitude and variability of nonadditive effects are, on average, respectively 5.8 and 1.8 times larger in moist (30% MC) species mixtures compared to dry (10% MC) mixed fuel beds. In general, the moist mixtures caused negative nonadditive effects, but due to the larger variability these mixtures occasionally caused large positive nonadditive effects, while this did not occur in dry mixtures. Thus, at moister conditions, mixtures occasionally pass the moisture threshold for ignition and fire spread, which the monospecific fuel beds are unable to pass. We also show that the magnitude of nonadditivity is highly species dependent. Thus, contrary to common belief, the strong nonadditive effects in mixtures can cause higher fire occurrence at moister conditions. This new integration of surface fuel moisture and species interactions will help us to better understand fire behavior in the complexity of natural ecosystems.

Ecologists traditionally use environmental parameters to predict successional shifts in compositional characteristics of local species assemblages (environmental control). Another important focus in ecology is to understand functional roles of species assemblages in determining local environmental properties (diversity control). Then, the question emerges: which is the cause, and which is the consequence? To clarify the causal relationships between species assemblages and environmental properties, we focused on seral changes in species/functional diversity of vascular plants in tundra ecosystems of the High Arctic. We found that, although species richness was influenced by soil properties in the earlier stages of primary succession, the causalities were reversed in the later stages. We also found functional differentiation among coexisting species in the later stage, suggesting that the ‘complementarity effect’ of diversity on ecosystem functions likely increased with ecosystem development through time. By contrast, particular species had little disproportional influence on soil properties, suggesting that the ‘selection effect’ as an alternative mechanism was less important. This result was likely attributed to the importance of facilitation in the marginal High Arctic environment. Plant–microsite associations are shaped by feedback mechanisms and therefore, neither plant nor microsite is a single absolute predictor of the other. Although our observational study has limitations, we demonstrates a possibility that the relative magnitude of the influence of one on the other can change in the process of succession, emphasizing that the causalities underlying biodiversity–ecosystem function relationships change through succession.

Despite the well-known importance of all elements to plant growth and nutrient fluxes in ecosystems, most studies to date have been restricted to the roles of foliar nitrogen (N) and phosphorus (P). Much less is known about cycling and pools of base cations in ecosystems and the drivers of variation in cation concentrations among plant species, even though these cations are paramount for plant and ecosystem function. In particular, little is known about the contributions of taxonomic position and environmental variation on base cation concentrations. The extent to which concentrations of elements in plants are determined by phenotypic response to their availability in current environments versus by inherent species-specific uptake and processing adaptations, should be most directly evident at the tips of the phylogeny, where inherent variation among species should reflect relatively recent adaptation to environmental variation since their common ancestry. To test this hypothesis, we explored the geographic pattern and the effects of taxonomy, climate and soil on concentrations and stoichiometry of the base cations potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) across a lineage of Artemisia species and their close relatives across northern China. We found that species identity explained the largest proportion of the total variance for all four base cations (38.3–53.8%) and their stoichiometry (35.2–59.6%). K, Na and Ca concentrations increased significantly with climate seasonality, while Ca concentration decreased with annual temperature and precipitation. Plant K concentration, K:Ca and K:Mg were negatively correlated with soil organic carbon concentrations, but positively with soil pH. Our results suggest that taxonomy still needs to be fully considered for interpreting variation in vegetation nutrition and stoichiometry along broad geographical gradients even for species at the tips of the phylogeny.