Yes, it does.
ZoneTree synchronizes the writes and reads internally and you don't have to worry about synchronization at all.
The following read/write methods are thread-safe:
ContainsKey, Upsert, TryGet, TryAdd, TryDelete, ForceDelete, Count

Please also consider the following in multi-threaded use-cases:

• Thread safety does not guarantee data consistency.
• Data consistency does not imply thread safety.