clean up species

[teixeirak]

Currently, we have scientific.name recording the scientific name ONLY FOR MONODOMINANT STANDS and veg.notes giving "Notes on the vegetation at time of measurement (e.g., forest type/ list of dominant species). For single species, field gives species name acronym, as listed in the USDA Plants Checklist (http://plants.usda.gov/dl_all.html)."

It would be preferable to have a single field listing species, and a separate field for USDA codes, if retained.