International Dendrological Research Institute
Nonprofit organization dedicated to documenting the woody flora worldwide.

Silvics of North America
Compendium of research papers describing the characteristics and distribution of important broadleaf and coniferous forest trees of the United States and Canada, plus many of the native and naturalized trees of Mexico, the Caribbean Islands, and Hawaii. Compiled over several decades by USDA Forest Service scientists.

The Ancient Bristlecone Pine
Dedicated to the oldest-known living tree, growing in the White Mountains in east central California. Information about the location, dendrochronology, photo gallery, and bibliography.

Tree Matters
Site for The Dendrologist, a quarterly magazine. Also contains tree tips and a record of the dates of upcoming dendrology events in the UK.

Tree Root Architecture
Information on research of tree root architecture, root excavation, 3D-digitising of root systems, tree root growth, tree stability, and windthrow.