public class World
{
    List<Item> _Items;
    public World()
    {
         // assign all the stuff, blah blahy
         _Items =  new List<Item>;
    }
 
    public AddItem(Item item)
    {
         _Items.Add(item);
    }
 
    public RemoveItem(Item item)
    {
        _Items.Remove(item);
    }
}
 
public class ItemActions
{
    public List<Action<Item>> _actions;
 
    public ItemActions()
    {
        _actions = new List<Action<Item>>();
    }
 
    public void AddAction(Action<Item> action)
    {
        _actions.Add(action);
    }
 
    public void ApplyAll(Item item)
    {
        foreach(Action action in _actions)
        {
             action(item);
        }
    }
}
 
public class ItemType
{
    // boring properties and more
    ItemActions onHarvest;
 
    public ItemType()
    {
        tree.properties = yada;
        tree.onHarvest = new List<Action>();
        tree.onHarvest.AddAction(delegate(Item i) { i.Parent.AddItem(new Item(Parent, ItemTypes.Log)); };
        tree.onHarvest.AddAction(delegate(Item i) { i.Remove(); };
    }
}
 
public class Item
{
    World Parent;
 
    public Item(World parent, ItemType itemtype)
    {
         Parent = parent;
         // assign properties from type, boring stuff.
         this.stuff = itemtype.stuff        
    }
 
    public void Remove()
    {
         Parent.RemoveItem(this);
    }
}
 
public class ItemHarvestable : Item
{
    ItemActions OnHarvest;
 
    public ItemHarvestable(World parent, ItemType itemtype) : base(parent, itemtype)
    {
        OnHarvest = itemtype.onHarvest;
    }
 
    public void Harvest()
    {
        OnHarvest.ApplyAll(this);
    }
}