# Environmental Effects on Normalized Gross Primary Productivity in Beech and Norway Spruce Forests
## 2 Materials and Methods
### Eddy Covariance and Ancillary Measurements  
At each station, the EC system consisted of an infrared gas analyzer (LI-COR, Lincoln, NE, USA) and an ultrasonic anemometer (Gill Instruments, Lymington, UK) measuring at 20 Hz frequency (detailed description in Table 11). Each system was mounted on a tower at height above the forest canopy (as specified in Table 11). EC measurements were complemented by an extensive set of sensors to collect the required auxiliary meteorological data.  
Measurements included air temperature (T\({}_{\mathrm{air}}\)) and relative humidity at the top of the forest canopy with the EMS33 temperature and humidity sensors (Embedded Moisture Sensor, Vancouver, BC, Canada). Hourly precipitation (P) was determined using a Precipitation Gauge 386C (Met One Instruments, Grants Pass, OR, USA). Measurements for the incoming photosynthetic active radiation (PAR) were made with a LI-190R Quantum Sensor (LI-COR, NE, USA) at both Billy Kriz and Stitna and with an EMS12 sensor (EMS, CZ) at Rajec. Additionally, profiles of soil moisture were measured using the CS616 (Campbell Scientific, North Logan, UT, USA) sensors at both spruce forest sites (in Bily Kriz and Rajec) and with the ThetaProbe (ML2x 355, Delta-T, Burwell, UK) sensors at Stitna. An overall description of the instrumentation at the study sites including soil temperature measurements (T\({}_{\mathrm{s}}\)) is given in Table 12.  
To analyze the effects of diffuse and direct radiation on daily mean GPP values, the dataset was divided into sunny and cloudy days based on the clearness index (CNI). CNI is defined as the ratio of solar irradiation transmitted through the atmosphere onto the Earth's surface relative to extraterrestrial irradiation. Sunny days were classified as days with CNI \(>\) 0.7 during daytime hours, cloudy days were characterized with CNI \(<\) 0.4, and CNI values of 0.4-0.7 were grouped as partly cloudy days [30].  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Site Name** & **CZ-BK1** & **CZ-RAJ** & **CZ-Stn** \\ \hline Location & Moravian-Silesian Beskids & Drahany Highland & White Carpathian \\  & Mountains & & Mountains \\ \hline Coordinates & 49\({}^{\circ}\)30\({}^{\prime}\)87\({}^{\circ}\) N, 18\({}^{\circ}\)32\({}^{\prime}\)15\({}^{\prime}\) E & 49\({}^{\circ}\)26\({}^{\prime}\)37\({}^{\prime\prime}\) N, 16\({}^{\circ}\)41\({}^{\prime}\)48\({}^{\prime\prime}\) E & 49\({}^{\circ}\)02\({}^{\prime}\)09\({}^{\prime\prime}\) N, 17\({}^{\circ}\)58\({}^{\prime}\)12\({}^{\prime\prime}\) E \\ \hline Elevation (in m a.s.l) & 875 & 625 & 540 \\ \hline \multirow{3}{*}{Topography} & Mountains (13” slope with SWS exposure, located close to a mountain ridge) & Hilly (5” slope with NNE exposure) & Mountainous (10” slope with WSW exposure) \\  & Coniferous evergreen forest & Coniferous evergreen forest & Deiculous broadleaf forest \\ \hline \multirow{3}{*}{Prevailing species} & Norway spruce (_Pican albis_ & Norway spruce (_Pican albis_ & European beach (_Fagus_ \\  & (L.) Karst.) & (L.) Karst.) & _sylutla L._) \\ \hline Canopy height (m) & 16 (mean, as of 2015) & 33 (mean, as of 2015) & 31 (mean, as of 2015) \\ \hline Stand age (years) & 35 (as of 2016) & 113 (as of 2016) & 115 (as of 2016) \\ \hline Mean seasonal air temperature (May-September, “C) & 14 * & 16 * & 17 * \\ \hline Total seasonal precipitation (May-September; mm) & 2730 * & 1635 * & 1719 * \\ \hline Seasonal sum of reference evapotranspiration (May-September; mm) & 2036 * & 2325 * & 2166 * \\ \hline Soil type & Haplic and Entic Podzol & Modal Cambisol & Eutric Cambisol \\ \hline References & [28] & [29] & [23] \\ \hline \hline \end{tabular}  
* 2012–2016 study period.  
\end{table}
Table 1: Characteristics of the investigated sites.  
The vapour pressure deficit (VDP; hPa) for each site was computed from Tair (\({}^{\circ}\)C) and relative air humidity (RH; %) according to [31]. The daily sum of PAR (MJ m\({}^{-2}\) day\({}^{-1}\)) was derived following the work in [32].