A grass has four times the relative growth rate of a tree. But it only has double the photosynthetic rate. Please explain why the grass has such a higher RGR.

Specific leaf area.

Explanation:

The grass has a higher relative growth rate as compared to trees because of Specific leaf area. The grass has higher growth rate due to their higher rate of photosynthesis which leads to more biomass production as compared to trees which takes too much time. The grass is able to grow faster due to environmental suitability or in other words, grasses has the ability to perform photosynthesis in every season and environment which the tree can't.