Examining the impact of shade on above-ground biomass and normalized difference vegetation index of C₃ and C₄ grass species in North-Western NSW, Australia

Abstract

Previous investigations have detected a directional trend in the normalized difference vegetation index (NDVI) of pastures around scattered paddock trees and identified shade from the tree as the most likely causal factor. This study uses a field experiment to quantify the effect of varying levels of shade on the above-ground biomass and NDVI of three grass species native to Australia ('Microlaena stipoides', C₃, shade tolerant; 'Austrodanthonia richardsonii', C₃, prefers full sunlight, and 'Chloris ventricosa', C₄, prefers full sunlight) in different seasons. The study demonstrates that shade had little influence on the above-ground biomass of C₃ species but significantly reduced biomass in the C₄ species. Until early winter, the NDVI of each species was generally significantly higher in all shaded treatments than in the no-shade treatment. This suggests that shaded plants retained a higher proportion of green biomass and/or changed leaf shape, increased leaf area and chlorophyll content. Regardless, although not proven in this experiment, it is likely shade prolonged the retention of green plant material into mid to late winter. Overall, this experiment explains the directional trends in NDVI around scattered trees found in previous work and suggests that shade from scattered trees prolongs green pasture production in a range of native grass species, without loss of C₃ pasture biomass.