What are dryads and pixies?

Dryads are tree fairies. Pixies are fungal fairies... and they have VERY different ways of viewing and experiencing the world. 

(For any who read this and see an inconsistency and/or plot hole... no you didn't. These are not absolute rules but rather... a bunch of opinions and subjective knowledge. There is no absolute truth nor one narrative here)

Dryads have physical forms, animalistic bodies that live and breathe within the physical plane. Their trees represent their 'subconscious mind' (although interpretations differ depending on who you ask. Ankh, for example, views one's connection to their tree as the single greatest determiner of one's morality and sanity, as they hold one's base emotion, consciousness and empathy.) Dryads as a whole used to name their tree with a complementary name, view their tree as a complementary entity and overall dryad society used to incorporate their trees into their identity, but alas, changing times and a tendency to forget.  

Pixies don't have separate fairy bodies. In fact, forget everything you know about dryads because none of that applies here.  

Also, their experience differs quite a bit from animals and dryads, so... yeah, it'll be a long one.  

Pixies are mental beings living 

When looking at mycorrhizal fungi, there's thousands of differing species within a single spoonful of soil, and scientists aren't sure if there's a distinct separation between one individual and another. So the pixie realm is more of a... Semi hive mind? The pixies do consider themselves a collection of  different organisms/their own society with their own customs rather than 'one pixie'. This is because some pixies have WIDLY different beliefs than others, (how do I explain this...). 

With mycorrhizal fungi, they both carry messages between trees that are further away from each other, and trade nutrients with trees. Mycorrhizal fungi gather nutrients like phosphorus and nitrogen and trade it for plant sugars. In pixie society, they highly covet these trades, because it's the only way they can lose/get new information out of their own choice. Otherwise, all the pixies do is rearrange and analyze the information already within their system.

(Think a university/ancient archives full of a bunch of academics that argue and debate about the books all day, overanalyzing the books and rearranging their shelves for easier organization. They're academics in every sense of the word... There are some pixies that don't covet information as much but they're a small minority, valuing information is the largest connecting factor.)  

 Soooo the hardest part to explain - with humans, each person has their own brain with their own experiences, along with their perspective of those experiences... And if you stop seeing people as their own entities, but rather vessels of the information in their brains... You got pixies. They don't really care about their identities or themselves as organisms/living beings. They are living breathing 'shelves of books', making notes in the margins and fusing and splitting as they see fit. You could view the information as memories more so. Except the pixies don't put any personal value on memories, memories are information and the thoughts attached to that experience.  

For example... An old trend of the pixies was analyzing the effects of 'this new human pest'. The pixies that became interested in this tended to have preexisting interests in nutrient composition near the surface of the soil, so they started to congregate amongst themselves. They don't really talk to share information. If they talk, if they use words, then they can misunderstand each other, misunderstand the information they cherish so much. So, pixies that experienced personal effects from human caused soil degradation fused to share their memories together, and spilt where they found the contradictions in memories could damage the information, creating a new pixies from the old ones. And because pixies fuse and split so often, they don't feel the need to have even an imaginary form. They're entirely abstract most of the time (incomprehensible to tree fairies, with their physical bodies. If a tree fairy were to contact and descend into the depths of the pixie archives, their brain couldn't process it, and they'd go crazy and/or die.)  

But some pixies stay as they are for a while, especially if they're fond of the tree and tree fairy they trade with and often talk to them with a more concrete form. Pixies don't form physical bodies... But they do create 'imaginary selves', 'mental forms' that look more like the dryads. These forms can either look like a fleshy body (completely imaginary though) or they look like a physical place. It depends on the pixie's preference. Some pixies hate the idea of pinning down their abstract nature into imaginary concepts. And before the whole 'pixie crisis' that happened before the story even starts, some pixies even fully left the pixie archives and nested within a tree fairy's brain. This was weird to most pixies, an outrage to others. Because if a pixie dies or leaves the system, the information they represented and held, all the memories and thoughts on those memories were lost forever.  

 Part of the point of the pixie archives is to be more incomprehensible... With some parts of it with more concrete and conceptual, other parts completely abstract. None of the POV characters are pixies so this realm isn't meant to be fully understood.