Query: Trees found in the Northwestern US, but not the Southwestern US
Domain: plants
Relevant documents:
Willamette Valley ponderosa pine
Populus balsamifera
Arbutus menziesii
Abies lasiocarpa
Alnus rubra
Western larch
Betula papyrifera
Carya washingtonensis
Juniperus occidentalis
Abies magnifica
Fraxinus pennsylvanica
Picea glauca
Abies procera
Frangula purshiana
Larix lyallii