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Question: Frequent severe wildfires have the potential to alter the structure and composition of forests in temperate biomes. While temperate forests dominated by resprouting trees are thought to be largely invulnerable to more frequent wildfires, empirical data to support this assumption are lacking. Does frequent fire erode tree persistence by increasing mortality and reducing regeneration, and what are the broader impacts on forest structure and understorey composition? Location: Sub-alpine open Eucalyptus pauciflora forests, Australian Alps, Victoria, Australia. Methods: We examined tree persistence and understorey composition of E. pauciflora open forests that were unburned, burned once, twice or three times by high-severity wildfires between 2003 and 2013. At each of 20 sites (five per fire frequency class) we assessed extent of top-kill and mortality of eucalypt clumps, spatial configuration of surviving and dead clumps, densities of new and lignotuberous eucalypt seedlings, and shrub and grass cover. Results: At least 2 yr after the last wildfire, proportions of top-killed E. pauciflora stems were significantly higher, and densities of live basal resprouts significantly lower, at sites burned two or three times compared to once burned or unburned sites. Clump death increased to 50% of individuals at sites burned by three short-interval wildfires, which led to changes in live tree patchiness, as indicated by nearest-neighbour indices. Increased tree mortality was not offset by seedling recruitment, which was significantly lower at the twice- and thrice-burned sites relative to single-burn sites – although seedling recruitment was also influenced by topography and coarse woody debris. In addition to changes in the tree layer, the prominence of understorey shrubs was substantially reduced, and the frequency of grasses markedly increased, after two, and particularly three wildfires. Conclusions: Our study provides strong empirical evidence of ecologically significant change in E. pauciflora forests after short-interval severe wildfires, namely, erosion of the persistence niche of resprouting trees, and a shift in understorey dominance from shrubs to grasses. Our findings highlight the need to consider the impacts of compounded perturbation on forests under changing climates, including testing assumptions of long-term persistence of resprouter-dominated communities.

Subalpine coniferous forest ecosystems are sensitive to climate change. However, the community formation mechanisms of subalpine coniferous forests in northeastern Asia remain poorly understood. In this study, we assessed the factors controlling the phylogenetic community structure in different strata (whole strata, upperstory, and understory) of Abies nephrolepis and Abies koreana forests in the subalpine zone in South Korea. Piecewise structural equation modeling (pSEM) was performed based on terrain, climate, taxonomic diversity, stand structure characteristics, and disturbance factors. The controlling factors presented different responses for each species depending on the stratum and phylogenetic community structure indices (net relatedness index and nearest taxon index). A. nephrolepis showed a unique community formation mechanism and formed climate refugia through high rock exposure, whereas A. koreana showed niche conservation at high elevations and a community overdispersion trend when forest gaps appeared due to overstory vegetation loss. The Mantel test and partial Mantel test were performed to examine the impact of turnover and nestedness on phylogenetic β‐diversity, as well as to establish their correlations with climatic, geographic, and environmental distance. Turnover was a major contributing factor to β‐diversity and strongly correlated with environmental distance. Further, geographical and climatic distance presented differential contributions to each species depending on the community characteristics. Integrated analyses of phylogenetic community structure and β‐diversity provided detailed insights into the mechanisms underlying community formation and biodiversity patterns. This reveals that biodiversity patterns are driven by interactions between community structure and inter‐community characteristics, with internal structure as a key mechanism influencing β‐diversity.

Aims: The 20th century has been marked by dramatic changes in land use, disturbance regimes and climate, which have interacted to affect global ecological patterns and dynamics, including changes in the extent, composition and structure of forest cover. Although much research has highlighted dramatic, short-term ecological change, on-going trends of land-use change and climate change began more than a century ago. Consequently, quantifying and understanding long-term (e.g. centennial) ecological change is critical to contextualizing recent patterns and processes. Here we document changes in the extent, position and composition of sub-alpine forests over the past century in eastern Switzerland. Location: Davos region of the Swiss Alps, eastern Switzerland. Methods: Position of tree line, forest cover and forest composition were evaluated using a unique combination of Object-Based Image Classification of an historical (1909) map, recent (2009) aerial photography and repeat terrestrial photography to minimize the inherent bias of each data source, while providing the most robust representation of long-term ecological change. Results: Over the past century total forest cover expanded by 64.6% and the position of sub-alpine tree line increased on all aspects. Total forest cover also increased at the highest and lowest elevations on all aspects. Dominance of European larch increased at the highest elevations, but decreased at the lowest elevations, where it was replaced by Norway spruce. These patterns suggest land use has been the most important driver of forest change over the past century. Conclusions: Major changes in the extent, structure and dynamics of sub-alpine forests in the Alps initiated earlier than previously documented and most change occurred prior to the middle of the 20th century. Furthermore, these changes were likely driven primarily by changes in land use, rather than by changes in climate. A combination of data sources and methodological approaches, such as those of the current study, provides a clearer view of long-term changes and minimize the biases associated with any single data source or methodology.

Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub‐alpine spruce forest, 1200–1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross‐dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30–60 years after tree death, when wood is in decay stages no. 4–7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.

We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an ‘extra’ day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixed-species stands.

Background and aims Coordination between leaf and root traits is crucial to plant performance and ecosystem functioning, but how leaves and roots coordinate in ectomycorrhizal (ECM)-dominated alpine forests remains unclear. Therefore, the covariation patterns of leaf and root traits of ECM-dominated alpine conifers and the environmental drivers were examined. Methods Five pairs of key leaf (i.e., leaf thickness [LT], specific leaf area [SLA], leaf tissue density [LTD], leaf N and P concentrations) and fine-root traits (i.e., root diameter [RD], specific root length [SRL], root tissue density [RTD], root N and P concentrations) were measured across 49 alpine coniferous populations (including 8 coniferous species) on the Tibetan Plateau. Results Root traits including RTD, root N and P concentrations and leaf traits such as LT, SLA, LTD, leaf N and P concentrations were correlated. The root-leaf relationships represent a tradeoff between resource conservation and fast plant growth, i.e., plant economic spectrum. RD and SRL were independent from the plant economic spectrum. Temperature drove variations in the leaf traits, RTD, root N and P concentrations, and conifers under low temperature had denser leaves and roots (i.e., larger LT, LTD, RTD) and lower nutrient contents. Precipitation primarily controlled variations in RD and SRL, and roots became thinner with decreasing precipitation. Conclusion Our study demonstrates divergent roles of temperature and precipitation in driving the coordination of leaf and root economic traits in the ECM-dominated alpine coniferous ecosystems. This is insightful for a comprehensive understanding of the adaptation and responses of alpine forests to climate change.

Background and aims Plant nitrogen (N) acquisition plays an important role in regulating plant growth and ecosystem functions. However, the seasonal variations in the relative contributions of different N sources to plant N uptake and how plants modify their N absorption preferences, especially in ectomycorrhizal forests, are not well understood. Methods We used the in situ 15 N-labeling method to quantitatively estimate the relative uptake contributions of plants for three different soil N sources (nitrate, ammonium and amino acids) and plant N acquisition preferences in an ectomycorrhizal alpine forest (a 70-year-old spruce plantation on the eastern Tibetan Plateau, China) during the growing season and the nongrowing season. Results Across the two seasons, plants in the spruce plantation showed a greater preference for acquiring soil NH 4 + -N, with soil NH 4 + contributing more than 50% to the total N uptake of plants (57.88% during the growing season and 52.72% during the non-growing season). Moreover, amino acids exhibited a considerable contribution to the total plant N uptake, and their contribution was significantly higher during the non-growing season (33.47%) than that during the growing season (9.86%). Accordingly, plants showed a greater preference for taking up amino acids over NO 3 − -N in the soil as the season changed from the growing season to the non-growing season. Conclusions Collectively, our data demonstrate that soil inorganic N is the predominant N source for plants in alpine forests, irrespective of seasonal variations. However, soil amino acids could also be an important supplementary N source for the plant N economy, especially during the non-growing season, when inorganic N availability is constrained. Our findings also suggest that plants in ectomycorrhizal alpine forests modify their nutrient absorption preference in response to seasonal changes.

PurposeIncreasing evidence suggests that the role of home-field advantage (i.e. HFA, the specialized decomposers efficiently degrade native litter) in altering decomposition is not restricted to low- or high-quality litter, we thereby hypothesized that different litter carbon (C) fractions may respond differently to these specialized decomposers, blurring the universality of HFA. Additionally, the inherent functional ability of local soil decomposers (i.e. ability) can influence litter decomposition.MethodsWe determined how the decomposition of litter dissolved organic C (DOC), total phenolics, cellulose, and lignin responded to HFA and ability in an alpine forest ecotone (i.e. coniferous forest, alpine shrubland, and alpine meadow).ResultsHFA influenced labile C, cellulose, and lignin decomposition, and its magnitude and direction depended on initial litter traits, particularly positively with litter C, nitrogen, phosphorus, DOC, and total phenolics concentrations. The effect of ability on labile C loss decreased from forest to meadow, consistent with the functional breadth hypothesis, suggesting that a wider ability from recalcitrant forest litter environment can accelerate labile C loss. The effect of ability on lignin degradation increased from forest to meadow, suggesting that the shift in forest and shrub species to meadow can decelerate biotic lignin degradation.ConclusionThe HFA occurrence is universal during decomposition, along with the distinct abilities were shaped by the altered plant compositions of mountain ecosystem, which has consequences for local plant-soil feedback by affecting litter decomposition.

Questions: What is the spatial range of regeneration of the fleshy-fruited tree Sorbus aucuparia (rowan) in a coarse-grained spruce stand on a large landscape scale? Does the spatial distribution and size of stands of different ages affect the probability of rowan regeneration? What are the consequences of the dynamics of dominant coniferous tree species for the dynamics of admixture rowan? Location: A sub-alpine spruce forest in the Tatra Mountains, Poland. Methods: We mapped all mature rowans in a 203-ha area and counted the rowan seedlings and saplings on a grid of evenly distributed plots. In plots, the age and diameter of trees were measured. Patches of homogenous stands were distinguished and each rowan tree and each plot was assigned to one of four stand categories: dense small-crowned stands, dense large-crowned stands, sparse large-crowned stands and sparse stands near the upper forest limit. Areas above the upper forest limit formed a separate fifth category. Results: The distribution of rowan trees was clumped. Most of them grew in dense spruce stands up to 135 yr old and near the upper forest limit. Substantially fewer rowan trees were in sparse spruce stands of nearly 200 yr old. Seedlings and saplings occurred at high density (mean 24.8 individuals 100 m⁻²) only up to 40 m from trees bearing fruits, and at much lower density at longer distances. In consequence of the clumped distribution of adult trees and the short range of seed dispersal, most of the old spruce stands were outside the range of abundant regeneration of rowan. Conclusions: The presence of fine- vs coarse-grained mosaics of coniferous stands of different ages can strongly influence population processes in a rowan population on a large landscape scale. Extensive disturbances resulting in large homogenous patches of coniferous stands, the long lifespan of a single generation of spruce and spatial limitation of rowan seed dispersal seem responsible for the small contribution this broad-leaved species makes to sub-alpine forests. A high share of rowan can be expected in forests with fine-grained mosaics of stands, where small patches of young and old stands are inter-mixed, assuring delivery of seeds to stands of each category.

Background Root activity creates a unique microbial hotspot in the rhizosphere, profoundly regulating soil activity and associated soil multifunctionality (SMF), the ability of soil to deliver multiple functions or services simultaneously. However, empirical studies on the characteristics of SMF in the rhizosphere and bulk soil and their microbial regulatory mechanisms remain scarce. Methods To address this gap, we conducted a field sampling campaign in an alpine forest on the eastern Tibetan Plateau. Soil abiotic and biotic properties, including soil nutrient availability, enzyme activities and microbial attributes were examined to compare the characteristics of SMF in the rhizosphere and bulk soil of Abies georgei , and to explore how microbial mechanisms drive SMF in each compartment. Results We found that the rhizosphere consistently exhibited higher SMF than bulk soil, highlighting its enhanced functional potential regardless of environmental variation. The relationship between microbial diversity and SMF was compartment-specific: bacteria diversity was strongly associated with SMF in the rhizosphere, while fungal diversity was closely linked to SMF in the bulk soil. Furthermore, microbial biomass, particularly fungal biomass, had a strong influence on SMF in both rhizosphere and bulk soils. Structural equation modeling revealed that the relationship between soil diversity and SMF were primarily mediated by variations in soil abiotic properties, including soil pH in the bulk soil, and soil moisture and clay content in the rhizosphere. Conclusions Our findings demonstrate that microbial contributions to soil multifunctionality are compartment-dependent and emphasize the need to integrate the rhizosphere perspective into biodiversity-multifunctionality frameworks for improving predictions of soil functions in terrestrial ecosystems.