First you will need lml
lml: https://www.rdr2mods.com/downloads/rdr2/tools/76-lennys-mod-loader-rdr/
Put ymaps here Red Dead Redemption 2\lml\stream
if you don't have the stream folder, create one inside lml (don't create it inside the download folder)
Put MacFarlane Vegetation on the LML dowloader folder/it is compatible with Project New Austin 1907 
if you have already downloaded it just put vegetationmodifiers.meta on the PNA1907 folder