Table 1.
Comparison of models predicting growing season productivity (GSP; estimated with integrated NDVI) using growing season length (GSL) and its interaction with clade and photosynthetic type.
Figure 1.
Differences in C3 and C4 start-of-season (SOS) (a), end-of-season (EOS) (b), growing season length (c), and growing season productivity (d).
Y-axis for panels (a)–(c) is the Julian day-of-year or DOY; y-axis for panel (d) is integrated NDVI, which is unitless, based on logistic models using 10-year timeseries of MODIS NDVI (see Methods). The growing season in Hawaii crosses the calendar year so that SOS begins at a later DOY than EOS. Most Poaceae species fall within the ‘BEP’ or ‘PACMAD’ clade. All C4 grasses are in the ‘PACMAD’ clade.
Figure 2.
The slope of the relationship between GSL and GSP differed for each photosynthetic type-clade combination (Model D, Table 2).
C3 PACMAD habitats exhibited higher rates of greenness than C4 PACMAD or C3 BEP habitats for a given growing season length (slope coefficients = 0.87, 0.83, and 0.59 respectively). Differences within the C3 functional group were larger than between photosynthetic pathways, i.e., there was a larger clade effect than photosynthetic pathway.
Table 2.
The relationship between growing season length (GSL) and productivity (GSP) (Model D in Table 1) was marginally different between C3 PACMAD and C4 grasses (GSL*clade:photosynthetic type), and significantly different between clades irrespective of photosynthetic type (GSL*clade). See Figure 2.