Just as we can describe communities made up of people by the kinds of people living in them communities made up of plants can be identified and characterized by the plants which comprise them. For example, you'd expect to find a people community made up largely of auto workers and their families in a area where there was automobile manufacturing. While there would also be people teaching in the schools, maintaining school grounds and facilities, others might work in local drug stores or grocery stores, and there would have to be a few working in government - and you can think of many more. People communities are complex. Plant communities and the interactions which take place in them are also complex.
Natural communities are certainly as complex as human communities.
For example, in a Pond pine community, you would expect to find a lot of pond pine trees. Underneath, smaller trees such as dahoon holly might be the next most abundant, and next most important. There might be a few sweetbay magnolia trees as tall as the dahoon holly, but not as many. Beneath these subcanopies are shrubby plants such as gallberry holly and saw palmetto. There are so many of them that you would have to count each of the different species to figure out which was more important.