From Guild Wars Wiki
Location in Morostav Trail
 Items dropped
- Even though he appears to be alone, six Warden of Seasons will popup when you get close to him. However, you can pull him aside while he's alone and the Warden of Seasons will only spawn if one of your allies go within earshot of Arbor's spawn location.
- The Warden of Seasons can also be pulled one at a time away from this boss if you prefer or they already spawned. Be sure to clear parts of the area around them though so you have a safe place to run to when needed.
- In hard mode, spread out the party before approaching this boss. The damage from Churning Earth and Shockwave can easily wipe the whole party.