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Figure 3


Estimation of the growing season start (SGS) for two sites from the CarboEurope network, Sodankylä, Finland (top) and Loobos, Netherlands (bottom). The upper curve illustrates CO2 fluxes observed above a Scots pine forest, while the lower one shows calculated stomatal conductances from the DO3SE model, when driven by temperature, irradiance and humidity only (i.e. no explicit phenological factor) (both in arbitrary units). The vertical lines illustrate the estimated SGS from four methods: (1) day when the mean 24-h temperature (T24) remains “permanently” (before midsummer) above 5 °C; (2) first day when T24 exceeds 5 °C for 5 consequtive days; (3) the default EMEP latitude model, SGS = 105 + 1.5(ϕ − 60), where ϕ is latitude; (4) the latitude-height function of Morén and Perttu (1994).

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