Well, they happen to be of central importance to most ecosystems - they form a vital link in the carbon cycle, breaking down and recycling plant matter.
(they; to be; of central importance) (they; form; a vital link in the carbon cycle) Context(they form,List([67, 76))):(they; happen; )
they form,List([67, 76))
they they they
to be form happen
of central importance
a vital link in the carbon cycle