The recent advancement of agent-based modeling is characterized by higher demands on the parameterization, evaluation and documentation of these computationally expensive models. Accordingly, there is also a growing request for "easy to go" applications just mimicking the input-output behavior of such models. Metamodels are being increasingly used for these tasks. In this paper, we provide an overview of common metamodel types and the purposes of their usage in an agent-based modeling context. To guide modelers in the selection and application of metamodels for their own needs, we further assessed their implementation effort and performance. We performed a literature research in January using four di erent databases. Five di erent terms paraphrasing metamodels (approximation, emulator, meta-model, metamodel and surrogate) were used to capture the whole range of relevant literature in all disciplines. All metamodel applications found were then categorized into specific metamodel types and rated by di erent junior and senior researches from varying disciplines (including forest sciences, landscape ecology, or economics) regarding the implementation e ort and performance. Specifically, we captured the metamodel performance according to (i) the consideration of uncertainties, (ii) the suitability assessment provided by the authors for the particular purpose, and (iii) the number of valuation criteria provided for suitability assessment. We selected distinct metamodel applications from studies published in peer-reviewed journals from to . These were used for the sensitivity analysis, calibration and upscaling of agent-based models, as well to mimic their prediction for di erent scenarios. This review provides information about the most applicable metamodel types for each purpose and forms a first guidance for the implementation and validation of metamodels for agent-based models.

No abstract

Background and Aims Trees interconnected through functional root grafts can exchange resources, but the effect of exchange on trees remains under debate. A mechanistic understanding of resources exchange via functional root grafts will help understand their ecological implications for tree water exchange for individual trees, groups of trees, and forest stands. Methods To identify the main patterns qualitatively describing the movement of sap between grafted trees, we reviewed available literature on root grafting in woody plants that focus on tree allometry and resource translocation via root grafts. We then extended the BETTINA model, which simulates mangrove (Avicennia germinans) tree growth on the individual tree scale, in order to synthesize the available empirical information. Using allometric data from a field study in mangrove stands, we simulated potential water exchange and analyzed movement patterns between grafted trees. Key Results In the simulations, relative water exchange ranged between -9.17 and 20.3 %, and was driven by gradients of water potential, i.e. differences in tree size and water availability. Moreover, the exchange of water through root grafts alters the water balance of trees and their feedback with the soil: grafted trees that receive water from their neighbors reduce their water uptake. Conclusions Our individual-tree modelling study is a first theoretical attempt to quantify root graft-mediated water exchange between trees. Our findings indicate that functional root grafts represent a vector of hydraulic redistribution, helping to maintain the water balance of grafted trees. This non-invasive approach can serve as a fundament for designing empirical studies to better understand the role of grafted root interaction networks on a broader scale.

Key message Plant–soil feedbacks in mangrove ecosystems are important for ecosystem resilience and can be investigated by establishing links between empirical and modelling studies. Abstract Plant–soil feedbacks are important as they provide valuable insights into ecosystem dynamics and ecosystems stability and resilience against multiple stressors and disturbances, including global climate change. In mangroves, plant–soil feedbacks are important for ecosystem resilience in the face of sea level rise, carbon sequestration, and to support successful ecosystem restoration. Despite the recognition of the importance of plant–soil feedbacks in mangroves, there is limited empirical data available. We reviewed empirical studies from mangrove ecosystems and evaluate numerical models addressing plant–soil feedbacks. The empirical evidence suggests that plant–soil feedbacks strongly influence ecological processes (e.g. seedling recruitment and soil elevation change) and forest structure in mangrove ecosystems. Numerical models, which successfully describe plant–soil feedbacks in mangrove and other ecosystems, can be used in future empirical studies to test mechanistic understanding and project outcomes of environmental change. Moreover, the combination of both, modelling and empirical approaches, can improve mechanistic understanding of plant–soil feedbacks and thereby ecosystem dynamics in mangrove ecosystems. This combination will help to support sustainable coastal management and conservation.

Abstract“Blue carbon” wetland vegetation has a limited freshwater requirement. One type, mangroves, utilizes less freshwater during transpiration than adjacent terrestrial ecoregions, equating to only 43% (average) to 57% (potential) of evapotranspiration ($$ET$$ ET ). Here, we demonstrate that comparative consumptive water use by mangrove vegetation is as much as 2905 kL H2O ha−1 year−1 less than adjacent ecoregions with $${E}_{c}$$ E c -to-$$ET$$ ET ratios of 47–70%. Lower porewater salinity would, however, increase mangrove $${E}_{c}$$ E c -to-$$ET$$ ET ratios by affecting leaf-, tree-, and stand-level eco-physiological controls on transpiration. Restricted water use is also additive to other ecosystem services provided by mangroves, such as high carbon sequestration, coastal protection and support of biodiversity within estuarine and marine environments. Low freshwater demand enables mangroves to sustain ecological values of connected estuarine ecosystems with future reductions in freshwater while not competing with the freshwater needs of humans. Conservative water use may also be a characteristic of other emergent blue carbon wetlands.

The occurrence of natural root grafts, the union of roots of the same or different trees, is common and shared across tree species. However, their significance for forest ecology remains little understood. While early research suggested negative effects of root grafting with the risk of pathogen transmission, recent evidence supports the hypothesis that it is an adaptive strategy that reduces stress by facilitating resource exchange. Here, by analysing mangrove root graft networks in a non-destructive way at stand level, we show further evidence of cooperation-associated benefits of root grafting. Grafted trees were found to dominate the upper canopy of the forest, and as the probability of grafting and the frequency of grafted groups increased with a higher environmental stress, the mean number of trees within grafted groups decreased. While trees do not actively ‘choose’ neighbours to graft to, our findings point to the existence of underlying mechanisms that regulate ‘optimal group size’ selection related to resource use within cooperating networks. This work calls for further studies to better understand tree interactions (i.e. network hydraulic redistribution) and their consequences for individual tree and forest stand resilience.

The occurrence of natural root grafts, the functional union of roots of the same or different trees1–3, is common and shared across tree species2. However, their significance for forest ecology remains little understood. While early research suggested negative effects of root grafting (i.e. increases the risk of pathogen transmission)4,5, recent evidence supports the hypothesis that it is an adaptive strategy that reduces stress6–8 by facilitating resource exchange9,10. Here by analysing mangrove root graft networks, we show evidence of cooperation-associated benefits of root grafting. Grafted trees were found to dominate the upper canopy of the forest, and as the probability of grafting and the frequency of grafted groups increased with a higher environmental stress, the mean group size (number of trees within groups) decreased. While root networks could form randomly (i.e. trees do not actively ‘choose’ neighbours to graft to)11,12, the increased frequency and reduced group sizes in higher-stress environments point to the existence of underlying mechanisms that regulate ‘optimal size’ group selection related to resource use within cooperating groups8,13,14. This work calls for further studies to better understand tree interactions (i.e. network hydraulic redistribution)15 and their consequences for individual tree and forest stand resilience and water-use efficiency.