The pilot of the tailwheel-equipped airplane reported that, during landing on a gravel runway, he noticed that the airplane "floated slightly off of the center of the runway to the west." The airplane touched down with the left wheel off the runway in some vegetation, and the airplane nosed over. Postaccident examination revealed that there were alder branches wrapped around the left main landing gear and that the landing gear was locked up. The pilot said he removed the branches, and the landing gear moved "fine." The airplane sustained substantial damage to the right wing lift strut and empennage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The pilot reported that the wind was from 090° and light and variable. The pilot landed the airplane on runway 33.