If humans killed ALL plants on earth, we would all suffocate. This is because plants convert co2 (carbon dioxide), which is exhaled by all animals, back into oxygen through photosynthesis. If they didn't convert co2, the earth's oxygen supply would depleat and we would fill the atmosphere with co2, and we would have no oxygen.
The populations of many animal species would decrease. We know that small animals live in this tundra ecosystem where there is little soil and fragile plants. If humans where to kill the plants and destroy the plants and land, then the animals would have no where to live. This would kill the mountain ecosystem.
An ecosystem is a place where plants and animals ( maybe humans ) live and animals and plants live in the desert so … 
there will be no ecosystem
humans, plants, cells, mammals, and insects.
The Earth's ecosystem would completely dissipate, and humans would not be able to survive, because there would be no food whatsoever.
if there is no plants humans cant get oxygen so naturally people cant exist on earth
Lack of oxygen production, the cycling of co2, and nutrients in the soil that need to be used that are essential for plant growth.
Humans would die, because plants make our oxygen
Other examples of the ecosystem are trees, water, plants, and humans. These are examples od an ecosystem because we rely on trees to give us oxygen, plants rely on us to give them Carbon dioxide, both trees and plants depend on water, and animals depend on plants to eat.
When herbivores are killed in a terrestrial ecosystem, it can disrupt the food chain and impact the population dynamics of other species. It may lead to overgrazing of plants, affecting vegetation growth and diversity. This can result in cascading effects on other organisms dependent on those plants for food or habitat.
There would be no oxygen therefore no humans or animals.
We wouldn't have any trees,fruit,vegetables or plants