Final answer:
The unmowed field would experience secondary succession, leading to a complex ecosystem with increased net primary productivity and biodiversity over time. Herbivores and other species would likely return as the area provides new sources of food and habitat.
Step-by-step explanation:
If no one mowed the grass at all, the field would undergo secondary succession. This type of ecological succession happens in areas where life has already existed and the soil is rich in nutrients. In the case of an unmowed field, the pioneer species like grasses would grow unchecked, and over time, other species such as shrubs and eventually trees might propagate, leading the area back to its natural state of a more complex ecosystem.
As for the mown field, the mowing action is what's preventing the grass from reproducing naturally. If the mowing were to stop, we might observe that the grasses would start flowering earlier as they adapt to the new conditions and need to reproduce. Mowing typically stabilizes the flowering time, creating a steady trend in the mowed field. Without mowing interference, the field's succession would accelerate as other flora and fauna return, increasing the net primary productivity and biodiversity of the area.
Eventually, herbivores that once lived in the area could return, looking for new sources of food provided by the flourishing plants, resulting in a rich interdependent ecosystem once again.