I think that the trees would be much more dense because Indiana is a naturally wooded state. The trees were obviously cleared when campus construction began, and because of this, (while there are still many trees on campus) there are far less trees than there would have been today. For example, I can easily pass through from one side of my nature site to the other, from Read Hall to the School of Education parking lot or from Forest Quadrangle to the Jordan Avenue Parking Garage. If humans had never come in contact with the site, I think the more dense foliage would have made it much harder to navigate and pass through this area.
Also, with more dense foliage comes more wildlife. While I have encountered birds like crows and starlings, squirrels, rabbits, and even a hawk in my nature site already, I think that there would be more deer and larger animals of that sort if humans had not cleared the area. As we see in rural, wooded areas of Indiana, there are larger populations of deer, coyotes, and wildcats than in those more urban areas with lesser amounts of trees and dense foliage. Only small rodents and typical "backyard" animals (like squirrels and rabbits) reside in much of suburban Indiana, and these are the types of animals I have mostly encountered in my nature site as of today.
Lastly, and most obviously, my nature site would not be surrounded by the physical structures that limit the space. Because my site is on a university campus, there are dormitories and education buildings that serve as the site's boundaries rather than natural boundaries that might have surrounded it before humans-- such as creeks or rock cliffs. Also, the area is highly accessible to humans, with paths running all around it and even a stone sitting area so that humans can sit and enjoy the space. Obviously, this area may be much more secluded and difficult to reach if the natural trees, brush, and foliage had not been cleared for the construction of university buildings.