Fig. 3. Cumulative volume and cumulative degree hours (> 5 °C) where ambient temperature was between 5 and 38 °C, photosynthetically active radiation (PAR) was greater than zero (daytime) and if nighttime temperatures were below 0 °C no hours are counted the next day for three sites (Virginia (VA), North Carolina (NC) and Brazil (BR)) where the same Pinus taeda genetic entries were planted at three initial densities (a). In Panel b cumulative degree hours were estimated as in Panel a and included an adjustment for vapor pressure deficit (VPD) where hours when VPD exceeded 1.5 kPa were not included. Regression lines for each sites are shown. Each point is a site mean.
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