Root systems store lots of CO2, protecting us from climate change. Open land and root systems absorb rains, protecting us from floods. Open land allows rainwater to refill underground aquifers. Plants produce oxygen. Home for pollinators which help our agricultural crops too.
If a species is too inbred, they could be more vulnerable to disease. They might not be able to handle changes in their environment well.
Species Diversity: all the different organisms on the planet!