Biometric, climate and site data collection will be carried out from 65 established stone pine Permanent sample plots (PSPs). These data will be essential for calibration and validation of the 3-PG process-based model, as well as to improve the existing modeling work done with Pinus pinea, which provides equations for estimates of cone occurrence and cone green weight. In addition, there will be a group of new plots established in the less productive stone pine stands. This will ensure that all Pinus pinea site productivity regions will be covered.
The 65 Pinus pinea Permanent Sample Plots were established and have been measured between 2004 and 2005 as well as in 2011. There have been cone collections on them annually from 2005 until 2008 (Freire 2009). These PSPs are already a considerable source of information for modeling growth and yield of stone pine; for instance the cone data have allowed the development of equations to estimate cone occurrence and cone weight. However more information is needed for calibration and validation of a process-based model. Such data are new measurements of height and diameter at breast height as well as information about soils, which involves assessing soil profiles in each plot, calculation of soil water holding capacity in the root zone and evaluation for soil nutrient status (the fertility rating parameter for 3-PG model). Stone pine PSPs are mainly concentrated in the most productive areas, which does not give a comprehensive picture of stone pine stands growing in Portugal. Therefore, a group from the existing plots will be deleted to avoid collecting redundant information, and some additional plots will be established in the less productive sites. Previous to the establishment of new plots a survey will be done in the less productive stone pine areas to ensure that a representative group of new sample plots will be selected. The information recorded on these sample plots will include standard forest biometric measurements. Weather data for the PSPs will be obtained from the network of weather stations of the National Meteorological Institute. These data include monthly average values of solar radiation, atmospheric vapor pressure deficit (VPD), rainfall, frost days per month and average temperature.