Potential variables forcing litterfall in a lower montane evergreen forest using Granger and superposed epoch analyses/ Prof. Dr. Dokrak Marod, Asst. Prof. Dr. Nisa Leksungnoen, Asst. Prof. Dr. Suwimon Uthairatsamee, Asst. Phruet Racharak, Asst. Prof. Dr. Tharnrat Kaewgrajang and Mr. Sathid Thinkamphaeng