[4] While professionally established, Hall went to work for ecologist Frederic Clements at the Carnegie Institution Division of Plant Sciences at Stanford University in 1919 in an effort to explore experimental methods of taxonomy.
[4] The pair established methods for conducting reciprocal transplant experiments, whereas plants were moved and studied in the habitats of similar taxonomic species.
[5] Hall left Clements group and started to assemble his own experimental team, hiring David Keck and William Hiesey in 1926 and Jens Clausen in 1931.
In 1928, Carnegie president John Merriam sent Hall to Europe for a year to study national parks.
His report suggested the creation of natural reserves with national parks for the purpose of scientific study.