What does a negative value of change in shoot biomass indicate?

It indicates the more destruction of plant population and number of predator is increasing.

Explanation:

The biomass is the dry weight of living organisms. The plant shoot biomass is the accurate measurement of plant biomass. It is the weight without water.

The biomass is calculated by drying any part of the plant in the oven and keep it in approximately 80-degree celsius. When all water is gone, it is measured and this weight is the biomass of the shoot.

The negative value of the biomass shows less weight of the plant. It is less than the actual weight. It happens when there is not enough space or enough food for the growth of the plants.

The negative value of biomass indicates there is rampant destruction of the plants and the number of predators is more.

Biomass is the total mass of a specific organism in the area. If there is a negative value of change in shoot biomass, that mean the mass of the shoot in this period are less than before. This indicate increases in predation/death which reduce the population of the shoot more than its growing rate. The cause could be an increases in predator population or decreases in food/resource.