The phrase "substantial decrease" means a significant or large decrease. It indicates that there has been a noticeable reduction in something, such as a decrease in value, quantity, or size. Full definition
«Future land transitions are uncertain but relatively small changes in afforestation from agriculture resulted in substantial decrease in accumulation rates,» said Coulston. (sciencedaily.com)
The study showed that temperature increases of 1 degree Celsius were associated with substantial decreases in both total crop area and double cropping. (sciencedaily.com)
«We saw substantial decreases at 2.5 percent of BA and nearly complete protection at the 10 percent concentration, strongly indicating that insect repellents with good safety profiles can be useful to reduce fruit damage during ripening.» (sciencedaily.com)