Net ecosystem exchange comparative analysis of the relative influence of recorded variables in well monitored ecosystems

Weekly averaged datasets from fourteen AmeriFlux ecosystem monitoring sites spread across the Americas, processed to the FLUXNET2015 standard, are statistically evaluated to characterize their seasonal net ecosystem exchange (NEE) trends. The sites cover wetland, cropland, woodland, grassland and tundra ecosystems. Up to twenty measured variables from the sites are variously correlated with NEE. A comparison of Pearson and Spearman correlation coefficients reveals that the variables are behaving parametrically with respect to NEE for the wetland, woodland (two out of three sites) and tundra locations, but non-parametrically for cropland and grassland sites. Multi-linear regression (MLR) analysis also distinguishes those ecosystems. MLR predicted versus calculated NEE follow Y ≈ X relationships for the wetland and tundra sites, whereas for the other ecosystems the MLR results follow Y≠X trends. Moreover, the coefficient values of the MLR optimum solutions for each ecosystem reveal quite distinct relative influences of the measured variables on the NEE predicted values. These results imply that NEE at wetland and tundra sites can be relatively easily predicted from the FLUXNET2015 set of recorded variables. On the other hand, the other three types of ecosystem sites cannot be easily predicted from those variables, implying that other factors substantially influence NEE at those sites.