Ancient Forest Exploration and Research
http://www.ancientforest.org/about-afer/

Minnesota’s Native Big Tree Registry
www.dnr.state.mn.us/trees_shrubs/bigtree/index.html

Heartwood
www.heartwood.org

Forest Ecology Network
www.forestecologynetwork.org

Ancient Forest International
https://www.treesfoundation.org/partners/afi/

Minnesota’s White Pines – The White Pine Society
www.whitepines.org

500-Year Forest Foundation
www.500yearforest.org

National Register of Big Trees
http://www.americanforests.org/our-programs/bigtree/

Native Tree Society
http://www.nativetreesociety.org

Wisconsin’s Champion Trees
http://dnr.wi.gov/topic/urbanforests/champion/

The Big Tree Society
http://www.unesco.org/new/en/doha/natural-sciences/the-big-tree-society/

Old-Growth Forest Network
http://www.oldgrowthforest.net

Society for the Protection of New Hampshire Forests
www.forestsociety.org