There’s lots of research onto foliage effects on RF propagation
http://www.jpier.org/PIERB/pierb17/08.09071901.pdf
https://www.ntu.edu.sg/home/eyhlee/Prof%2520Lee/PIER%2520foliage%2520review%25202010.pdf
https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.833-9-201609-I!!PDF-E.pdf