What is the main similarity between grassland and tundra ecosystems?

Neither is very cold.

Both suffer from frequent wildfires.

Both provide fertile land for farming.

Neither has a single, dominant vegetation.

We have to say that is neither has a single, dominant vegetation. In both cases none of them suffer from wildlife, actually they are habitat of many of them. Those are parts where there can not be farming and actually one of them is very cold. So thats why we can go with the last option