Timescale effects on the environmental control of carbon and water fluxes of an apple orchard. Issue 1 (29th November 2017)

• Record Type: Journal Article
• Authors: Montagnani, Leonardo; Zanotelli, Damiano; Tagliavini, Massimo; Tomelleri, Enrico
• Is Part Of: Ecology and evolution. Volume 8:Issue 1(2018)
• Page Start: 416
• Page End: 434
• Publication Date: 2017-11-29
• Subjects: environmental constraints -- evapotranspiration -- hysteresis -- modeling -- net ecosystem exchange -- phase -- timescales; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.3633
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Model parameterization and validation of earth–atmosphere interactions are generally performed using a single timescale (e.g., nearly instantaneous, daily, and annual), although both delayed responses and hysteretic effects have been widely recognized. The lack of consideration of these effects hampers our capability to represent them in empirical‐ or process‐based models. Here we explore, using an apple orchard ecosystem in the North of Italy as a simplified case study, how the considered timescale impacts the relative importance of the single environmental variables in explaining observed net ecosystem exchange (NEE) and evapotranspiration (ET). Using 6 years of eddy covariance and meteorological information as input data, we found a decay of the relative importance of the modeling capability of photosynthetically active radiation in explaining both NEE and ET moving from half‐hourly to seasonal timescale and an increase in the relative importance of air temperature ( T ) and VPD. Satellite NDVI, used as proxy of leaf development, added little improvement to overall modeling capability. Increasing the timescale, the number of variables needed for parameterization decreased (from 5 to 1), while the proportion of variance explained by the model increased ( r 2 from 0.56–0.78 to 0.85–0.90 for NEE and ET respectively). The wavelet coherence and the phase analyses showed that the two variables that increased their relative importance when the scale increased ( T, VPD) were not in phase at the correlation peak of both ET and NEE. This phase shift in the time domain corresponds to a hysteretic response in the meteorological variables domain. This work confirms that the model parameterization should be performed using parameters calculated at the appropriate scale. It suggests that in managed ecosystems, where the interannual variability is minimized by the agronomic practices, the use of timescales large enough to include hysteretic and delayed responses reduces the number of required input variables and improves their explanatory capacity. Abstract : Model parameterization and validation of earth–atmosphere interactions are generally performed using a single timescale, although both delayed responses and hysteretic effects have been widely recognized. We quantified the relative importance of a set of environmental drivers influencing NEE and ET in an apple orchard, and we observed that it was changing over time. The relative importance of PAR was reducing increasing the timescale, in favor of T and VPD, and their explanatory capability increased. This study suggests that in agricultural ecosystems when parameterizing variables showing hysteretic effects with ecosystem fluxes it is convenient to enlarge the integration period up to the timescale of interest.