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

Abstract

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.