Are resource nodes (ore, wood, herbs) instanced

Resource nodes seem to work in three seperate ways.

1. There are what the devs call "Node farms", groups of 8-10 of the same resource in a small area. These respawn after 23 hours (so people who play at roughly the same time don't have to worry about being a few minutes ahead of 24 hours). These are mostly or entirely food items.

2. There are what I'm going to call "Placed Nodes" which are specifically located, normally rich nodes guarded by veteran or champion enemies, or requiring the completion of an event to access. These also appear to respawn after 23 hours.

3. There are what I'm going to call "wild nodes", located randomly in the wilderness. Most nodes fall under this category. These nodes do not respawn after 23 hours. Instead, wild nodes appear and disappear gradually over time. After a few hours of play, you can return to an area that was previously cleared and see plenty of nodes. Those are wild nodes. however, you will notice that they are not in exactly the same location as the nodes you previously cleared, as they are different nodes that appears, just in similar locations. This means that an area will gradually become more and more abundant overtime, until all the old nodes you harvested are removed and replaced by newer, full ones. I believe that it takes between 8-24 hours for an area to fully replenish its wild node density. However, a new node can appear on your map within a few minutes of harvesting a nearby node.

I haven't seen an answer from Arenanet on this one, but I believe it depends on what type of node you're gathering from. Ore nodes, for example, all appear to have approximately a 20% chance per hit to receive gemstones, while gathering nodes have a much lower chance to yield an unidentified dye (likely to be about 1%).

From my experience, tools labeled as "more efficient" or "extremely efficient" only make a small difference to the total drop rate of rare components.

It is also noteworthy that such tools seem to have a higher chance to preserve the node that was gathered from rather than destroying it, although this chance is still low.