"start" -- first year
of outbreak
"end" -- last year of outbreak
"duration" --
length of outbreak (in years)
"n_df_start" -- number of trees
defoliated at the start
"perc_df_start" -- percent of trees
defoliated at the start
"max_df_obr" -- maximum number of trees in
the outbreak during a single year
"yr_max_df" -- year with the
maximum number of trees defoliated
"yr_min_ngsi" -- year with the
lowest mean normalized growth suppression index (NGSI)
"min_gsi" --
minimum growth suppression index
"min_ngsi" -- minimum normalized
gsi