Estimating the relative abundance of C₃ and C₄ grasses in the Great Plains from multi-temporal MTCI data: issues of compositing period and spatial generalizability

Accommodating for the differences between grasses following the C3 and C4 photosynthetic pathways in environmental research often requires information on their spatial distribution and relative abundance. Multi-temporal remote sensing may indicate the latter because these grasses have asynchronous phenologies. The relationship between remotely sensed variables and grassland composition, defined by C3(%), was explored with attention focused on two key issues associated with studies of large areas from multi-temporal datasets: the compositing period used and spatial generalizability of a selected relationship. MERIS Terrestrial Chlorophyll Index (MTCI) composites of the Great Plains were generated using compositing periods of 5, 7, 10 and 14 days. The results of a regression analysis indicated that a relationship between MTCI data and grassland composition may be formulated for the State of South Dakota with R 2 ∼0.6. The strength of the relationship was, generally, strongest for short compositing periods. The transferability of the relationship to other regions was, however, limited by its significant non-stationarity indicating a challenge for large area studies. Acknowledgements This work was supported by the NERC QUEST programme (NE/C516187/1, QUERCC). The GWR analyses were undertaken with the GWR3.0 software. MERIS data were obtained from ESA and 8-day MTCI composites were obtained from the NERC EODC. We are grateful to the referees for their helpful comments on the article.