The terrestrial carbon (C) cycle has been commonly represented by a series of C balance equations to track C influxes into and effluxes out of individual pools in earth system models (
Numerous current efforts seek to improve the representation of ecosystem ecology and vegetation demographic processes within Earth System Models (
- NSF-PAR ID:
- 10045664
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 24
- Issue:
- 1
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 35-54
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ESM s). This representation matches our understanding of C cycle processes well but makes it difficult to track model behaviors. It is also computationally expensive, limiting the ability to conduct comprehensive parametric sensitivity analyses. To overcome these challenges, we have developed a matrix approach, which reorganizes the C balance equations in the originalESM into one matrix equation without changing any modeled C cycle processes and mechanisms. We applied the matrix approach to the Community Land Model (CLM 4.5) with vertically‐resolved biogeochemistry. The matrix equation exactly reproduces litter and soil organic carbon (SOC ) dynamics of the standardCLM 4.5 across different spatial‐temporal scales. The matrix approach enables effective diagnosis of system properties such as C residence time and attribution of global change impacts to relevant processes. We illustrated, for example, the impacts ofCO 2fertilization on litter andSOC dynamics can be easily decomposed into the relative contributions from C input, allocation of external C into different C pools, nitrogen regulation, altered soil environmental conditions, and vertical mixing along the soil profile. In addition, the matrix tool can accelerate model spin‐up, permit thorough parametric sensitivity tests, enable pool‐based data assimilation, and facilitate tracking and benchmarking of model behaviors. Overall, the matrix approach can make a broad range of future modeling activities more efficient and effective. -
Abstract Aims Bryophytes can cover three quarters of the ground surface, play key ecological functions, and increase biodiversity in mesic high‐elevation conifer forests of the temperate zone. Forest gaps affect species coexistence (and ecosystem functions) as suggested by the gap and gap‐size partitioning hypotheses (
GPH ,GSPH ). Here we test these hypotheses in the context of high‐elevation forest bryophyte communities and their functional attributes.Study Site Spruce–fir forests on Whiteface Mountain, NY,
USA .Methods We characterized canopy openness, microclimate, forest floor substrates, vascular vegetation cover, and moss layer (cover, common species, and functional attributes) in three canopy openness environments (gap, gap edge, forest canopy) across 20 gaps (fir waves) (
n = 60); the functional attributes were based on 16 morphologic, reproductive, and ecological bryophyte plant functional traits (PFT s). We testedGPH andGSPH relative to bryophyte community metrics (cover, composition), traits, and trait functional sensitivity (functional dispersion;FDis ) using indicator species analysis, ordination, and regression.Results Canopy openness drove gradients in ground‐level temperature, substrate abundance and heterogeneity (beta diversity), and understory vascular vegetation cover. The
GPH was consistent with (a) the abundance patterns of forest canopy indicator species (Dicranum fuscescens ,Hypnum imponens , andTetraphis pellucida ), and (b)FDis based on threePFT s (growth form, fertility, and acidity), both increasing with canopy cover. We did not find support forGPH in the remaining species or traits, or forGSPH in general; gap width (12–44 m) was not related to environmental or bryophyte community gradients.Conclusions The observed lack of variation in most bryophyte metrics across canopy environments suggests high resistance of the bryophyte layer to natural canopy gaps in high‐elevation forests. However, responses of forest canopy indicator species suggest that canopy mortality, potentially increased by changing climate or insect pests, may cause declines in some forest canopy species and consequently in the functional diversity of bryophyte communities.
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Abstract This study asks whether the spatial scale of sampling alters structural properties of food webs and whether any differences are attributable to changes in species richness and connectance with scale. Understanding how different aspects of sampling effort affect ecological network structure is important for both fundamental ecological knowledge and the application of network analysis in conservation and management. Using a highly resolved food web for the marine intertidal ecosystem of the
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Abstract In semiarid regions, vegetation constraints on plant growth responses to precipitation (
PPT ) are hypothesized to place an upper limit on net primary productivity (NPP ), leading to predictions of future shifts from currently defined linear to saturatingNPP –PPT relationships as increases in both dry and wetPPT extremes occur. We experimentally tested this prediction by imposing a replicated gradient of growing seasonPPT (GSP ,n = 11 levels,n = 4 replicates), ranging from the driest to wettest conditions in the 75‐yr climate record, within a semiarid grassland. We focused on responses of two key ecosystem processes: abovegroundNPP (ANPP ) and soil respiration (R s).ANPP andR sboth exhibited greater relative responses to wet vs. dryGSP extremes, with a linear relationship consistently best explaining the response of both processes toGSP . However, this responsiveness toGSP peaked at moderate levels of extremity for both processes, and declined at the most extremeGSP levels, suggesting that greater sensitivity ofANPP andR sto wet vs. dry conditions may diminish under increased magnitudes ofGSP extremes. Underlying these responses was rapid plant compositional change driven by increased forb production and cover asGSP transitioned to extreme wet conditions. This compositional shift increased the magnitude ofANPP responses to wetGSP extremes, as well as the slope and variability explained in theANPP –GSP relationship. Our findings suggest that rapid plant compositional change may act as a mediator of semiarid ecosystem responses to predicted changes inGSP extremes. -
Abstract Ecological communities are structured by a combination of local processes like habitat filtering and species interactions, and regional forces driven by the dispersal of organisms between localities on a landscape. Previous studies suggest that the position of local communities within a dispersal network can greatly influence the relative influence of these two sets of processes on community assembly. However, the majority of previous investigations have used models or inferences based on observational data to investigate these hypotheses, while experiments directly addressing this question have been rare.
We experimentally investigated the relative influence of local and regional processes in structuring benthic invertebrate communities using artificial streams. We manipulated three factors—source pool for the macroinvertebrate community (headwater vs. mainstem) as a surrogate of network location, habitat complexity (high vs. low) in the flume, and dispersal (high vs. low)—and followed changes in macroinvertebrate community structure for 8 weeks.
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HW source pools, the high dispersal treatment had significantly higher diversity than low dispersal flumes. However, this difference only occurred in flumes withHW source pools and did not occur in flumes withMS sources. There was also strong evidence of community composition inHW flumes shifting significantly towards the macroinvertebrate composition in our experimental dispersal treatment. The major effect of experimental dispersal was to introduce new species in fairly low abundances as would be expected from dispersal via drift over a relatively short time. BothMS andHW colonised flumes showed highly significant signals of habitat filtering, though the influence of specific habitat differed between the source types.These results support the hypothesis that dispersal driven processes are a more important structuring force in well‐connected areas of networks by experimentally demonstrating the responsiveness of previously isolated communities to experimentally induced dispersal. They also demonstrate that this responsiveness is not due to an inherent difference in habitat affinity since source communities from both
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