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Restoration is moving towards a more mechanistic approach that emphasizes restoration of ecosystem services. Trait-based approaches provide links between species identity and ecosystem functions and have been suggested as a promising way to formally integrate ecosystem services in the design of restoration programs. While practitioners have been routinely using informal knowledge on plant traits in their practices, these approaches are underutilized as operationalization remains challenging. The goal of this paper is to provide guidance for applied scientists and restoration practitioners looking to apply a trait-based approach to restore forest ecosystems. We present a five-step framework: (1) selection of services to be restored, (2) trait selection, (3) data acquisition, (4) analytical planning, and (5) empirical testing and monitoring. We use three Canadian case studies to illustrate the applicability of our framework and the variety of ways trait-based approaches can inform restoration practices: (1) restoration of urban woodlots after an insect outbreak, (2) restoration of a smelter-damaged landscape surrounding an urban area, and (3) reclamation of remote upland forests after oil- and gas-related disturbances. We describe the major mechanisms and traits that determine vegetation effects on ecosystem services of importance in each case study. We then discuss data availability, methodological constraints, comparability issues, analytical methods, and the importance of empirical testing and monitoring to ensure realistic prediction of service restoration. By outlining issues and offering practical information, we aim to contribute to a more robust use of traits in ecological restoration. [ABSTRACT FROM AUTHOR]

From soil to freshwater ecosystems, decomposition can be conceived as the result of interactions between organic matter and a diversity of organisms. This function is driven in part by detritivores, invertebrates that feed on detritus or graze on its associated microbes and that have a significant but extremely variable contribution to decomposition.In order to better understand and predict detritivore–detritus pairwise interactions, we propose a conceptual framework, called Detri2match, to study the consumption of detritus by detritivores, using a trait‐matching approach at the individual detritivore level. Here, we focus on the interaction between saprophagous detritivores that fragment plant detritus.We propose a novel definition of a saprophagous detritivore as an animal that consumes plant detritus when its traits match sufficiently the traits of its resource, passing through five interaction facets of consumption. These include (1) a spatial match rule regarding the encounter, (2) a biomechanical match rule regarding ingestion, (3) a digestive match rule regarding assimilation, (4) an energetic match rule regarding the fulfilment of metabolic needs and (5) a nutritional match rule regarding the fulfilment of chemical element needs in adapted proportions.The main goal of this framework is to guide future research to establish generic rules of misunderstood detritus–detritivore pairwise interactions by identifying relevant interaction facets and their key associated traits for both detritivores and detritus. This investigation should be conducted over the temporal variability of trait‐matching constraints throughout the whole decomposition process. Coupled with adequate accumulation of trait information, the Detri2match framework could also facilitate predictions by inference of non‐tested pairwise detritivore–litter interactions.We also outline conceptual, methodological and analytical challenges of this framework. The main challenge would be to scale up these pairwise rules at the detrital network level and to test their genericity, which would contribute to a better understanding of the functioning of the detrital network and its contribution to decomposition. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Outbreaks of defoliator insects are important natural disturbances in boreal forests, but their increasing frequency under warming climate conditions is of concern. Outbreak events can shape ecosystem dynamics with cascading effects through trophic networks. Caterpillar defoliation can alter tree physiology, increase sunlight to the understory, and result in the deposition of large amounts of leaf litter and caterpillar frass to the forest floor. These modifications can thus affect soil organisms through direct (e.g., changes in soil temperature or moisture) or indirect (e.g., changes in detrital and root food webs) mechanisms. We assessed whether a recent (2015 to 2017) outbreak of the forest tent caterpillar (Malacosoma disstria) at the Lake Duparquet Teaching and Research Forest (Abitibi, QC, Canada) affected soil springtail communities, abundant microarthropods in forest soils. In 2018 and 2019, we sampled litter and soil (0–10 cm depth) at eight sites each in aspen-dominated (Populus tremuloides Michx) stands that were undefoliated or had a recent defoliation history. We found no significant difference in springtail abundance (specimens cm−2) or alpha diversity indices between undefoliated sites and those with defoliation history. However, we observed a transient change in springtail community composition 1 year after the outbreak (2018) with the absence of Folsomia nivalis, Anurophorus sp1, and Xenylla christianseni in sites with defoliation history, but no compositional differences were observed in 2019. Certain soil nutrients (P, C, Mg, Mn) were significant predictors of springtail community composition, but soil microbial biomass was not, despite its significant decrease in sites with defoliation history. Our results show that soil springtail communities respond in the short-term to the forest tent caterpillar outbreak with compositional shifts, but seem ultimately resilient to these events. [ABSTRACT FROM AUTHOR]

The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere (1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs (2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical (4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being (7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition (4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism (4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales., Biological diversity that directly influences litter decomposition exists at multiple trophic levels (4). This diversity includes plants that produce litter mixtures of varying quality, microbial decomposers and invertebrate consumers of [...]

Historically, carbon limitation, through a shortage of photoassimilates has been argued to limit the growth of trees at the upper altitudinal treeline. In a three-year free-air C[O.sub.2] enrichment (FACE) experiment, two species of 30-year-old alpine conifers (Larix decidua and Pinus uncinata) were studied to test this hypothesis in situ in the Swiss Central Alps (2180 m above sea level). C[O.sub.2] enrichment was combined with foliage removal to test the effect of altered source-sink relationships on tree growth and leaf level responses. Elevated C[O.sub.2] enhanced photosynthesis and increased nonstructural carbohydrate (NSC) concentrations in the needles of both species. While the deciduous larch trees showed longer needles and a stimulation of shoot growth over all three seasons when grown in situ under elevated C[O.sub.2], pine trees showed no such responses. Irrespective of C[O.sub.2] concentration, defoliation in both species stimulated photosynthesis and increased stomatal conductance in remaining current-year needles in the treatment year and reduced leaf nitrogen concentration in the year following defoliation. Defoliated larch trees had fewer and shorter needles with reduced NSC concentrations in the year following defoliation and showed no stimulation in shoot elongation when exposed to elevated C[O.sub.2]. In contrast, defoliation of evergreen pine trees had no effect on needle NSC concentrations, but stimulated shoot elongation when defoliated trees were exposed to elevated C[O.sub.2]. After three years, our results suggest that deciduous larch is carbon limited at treeline, while evergreen pine is not. However, as indicated by the defoliation treatment, the carbon economy of these trees can clearly be modified by extreme events. The expected changes in growth of these treeline trees with improving carbon availability as atmospheric C[O.sub.2] continues to increase will thus depend on both the interplay between biotic and abiotic processes, and the species or tree functional types involved. Key words: alpine; biodiversity; elevated C[O.sub.2]; Larix decidua; Pinus uncinata; shoot growth; source--sink balance; timberline.

1. Plants are frequently observed to increase carbon allocation to below-ground sinks and particularly, to accelerate fine root turnover in response to rising atmospheric CO2 concentration. While these strong below-ground responses have predominantly been observed in rapidly expanding systems, late successional plant communities have rarely been studied. 2. In an ongoing free air CO2 enrichment (FACE) experiment, we assessed below-ground responses to elevated CO2 after 4 years, in a treeline ecosystem in the Swiss Central Alps (2180 m a.s.l.) dominated by a late successional ericaceous dwarf shrub community ( Vaccinium myrtillus, V. uliginosum, Empetrum hermaphroditum), and a sparse overstorey of 30-year-old Larix decidua and Pinus uncinata trees. Measurements included quantification of fine root growth using ingrowth root cores and parallel standing crop harvests and decomposition of roots using litter bags. 3. Elevated CO2 did not stimulate root growth of the treated vegetation (although some significant above-ground growth responses were observed), nor did altered root decomposition occur. Root quality measurements indicated that elevated CO2 resulted in significantly higher starch concentrations, but no change in N concentration, or root dehydrogenase activity. 4. The use of the stable isotope δ13C permitted us to trace the new carbon entering the system through our CO2 enrichment treatment. We observed that only c. 30% of new root biomass (< 2 mm) was formed by new carbon indicating a rather slow root turnover in this system. 5. Our data show that fine root growth may be much less stimulated by elevated CO2 in systems with late successional elements than has been reported in ecosystems with a rapidly expanding plant community biomass. [ABSTRACT FROM AUTHOR]

Historically, carbon limitation, through a shortage of photoassimilates has been argued to limit the growth of trees at the upper altitudinal treeline. In a three-year free-air CO2 enrichment (FACE) experiment, two species of 30-year-old alpine conifers (Larix decidua and Pinus uncinata) were studied to test this hypothesis in situ in the Swiss Central Alps (2180 m above sea level). CO2 enrichment was combined with foliage removal to test the effect of altered source-sink relationships on tree growth and leaf level responses. Elevated CO2 enhanced photosynthesis and increased nonstructural carbohydrate (NSC) concentrations in the needles of both species. While the deciduous larch trees showed longer needles and a stimulation of shoot growth over all three seasons when grown in situ under elevated CO2, pine trees showed no such responses. Irrespective of CO2 concentration, defoliation in both species stimulated photosynthesis and increased stomatal conductance in remaining current-year needles in the treatment year and reduced leaf nitrogen concentration in the year following defoliation. Defoliated larch trees had fewer and shorter needles with reduced NSC concentrations in the year following defoliation and showed no stimulation in shoot elongation when exposed to elevated CO2. In contrast, defoliation of evergreen pine trees had no effect on needle NSC concentrations, but stimulated shoot elongation when defoliated trees were exposed to elevated CO2. After three years, our results suggest that deciduous larch is carbon limited at treeline, while evergreen pine is not. However, as indicated by the defoliation treatment, the carbon economy of these trees can clearly be modified by extreme events. The expected changes in growth of these treeline trees with improving carbon availability as atmospheric CO2 continues to increase will thus depend on both the interplay between biotic and abiotic processes, and the species or tree functional types involved. [ABSTRACT FROM AUTHOR]

Summary • Experimental CO2 enrichment of mature Larix decidua and Pinus uncinata trees and their understory vegetation was used to test the carbon limitation hypothesis of treeline formation at the alpine treeline in Switzerland. • Forty plots (each 1.1 m2 ) were established; half of them were exposed to elevated (566 ppm) atmospheric CO2 using a free air CO2 enrichment (FACE) system releasing pure CO2 , and the other half were treated as controls at current ambient [CO2 ]. • Reliable and adequate CO2 control was achieved, with 63% and 90% of 1-min averages having a [CO2 ] within ±10% and ±20% of the target value, respectively, which is comparable to previous FACE systems. Both tree species showed higher net photosynthesis, lower stomatal conductance, and increased accumulation of nonstructural carbohydrates in response to CO2 in the first year of treatment. Quite unexpectedly, shoot length increment increased significantly at elevated CO2 (up to 23%) compared with controls in both species. • The pure CO2 release technology proved suitable for CO2 enrichment of native trees on this remote mountain slope. Our results suggest an improved C balance and growth of treeline trees in response to elevated CO2 . However, it is unclear whether this initial growth stimulation will persist in the longer term. [ABSTRACT FROM AUTHOR]