The vegetation along Upper Cascadilla varies considerably in composition and quality; it includes upland forest, shrub thicket, wetland and floodplain forest. South of the Cornell Orchards, on the dry, south-facing slopes, there are several good examples of mature oak-hickory forest. Some of these hickories were planted and grafted by L. H. MacDaniels and his students. Some rare, important old nut tree cultivars still exist here. Click here for more information.
South of the railroad right-of-way, about mid-way between Pine Tree Road and Game Farm Road, there is a beautiful mature floodplain forest with sycamores and cottonwoods and a very rich herb layer. On the north-facing slopes, white pine and hemlock are abundant. Red maple and white pine dominate the forests on areas that were once agricultural fields.
Along parts of the recreation way, the vegetation is weedy and scruffy. In places the creek bank is severely eroding. The large grassy open area along the trail was once a Cornell landfill and has been capped relatively recently. The wetlands on the north side of the trail were probably first drastically altered when the railroad was built. Recently one of the wetland areas along the trail was re-constructed, removing accumulated sediments and re-introducing native plant species. Although not very diverse, such constructed wetlands can be of significant value in protecting water quality. The high water quality in Cascadilla Creek makes it an important resource for research and teaching. Aquatic entomology and stream ecology classes use it regularly. Because the creek is so clean, it has great biodiversity: many species of freshwater insects and fish. The ponds near the fisheries lab are an especially good area for birding.