Dryads

“Curse him, root and branch! Many of those trees were my friends, creatures I had known from nut and acorn; many had voices of their own that are lost forever now. And there is a waste of stump and bramble where once there were singing groves. I have been idle. I have let things slip. It must stop!”

— J.R.R. Tolkien, The Two Towers

The dryads are beings of life and nature that grow and dwell far from civilisations. They may look like gnarled trees and brambles but rouse their ire and they shall teach you such appearances can be deceiving.
They are also kalled "tree-men" or "tree-kin"

Description

Dryads are born from old places of of great age and life, such as ancient forests and jungles. In such places, nature magic ebbs and flows and accumulates over centuries and millennia. The energy of life will filter down into the beings in the area and raise them onto a higher state of being. The trees will wake and wander, gaining sapience and an innate understanding of the ways of Nature Magic and life.

Small and 'young' dryads can be relatively weak and inexperienced, while ancient gnarled tree-kin can be fearsome foes to all but the most legendary of heroes. They can posess both physical and magical might, in addition to great cunning and experience.

Dryads are old beings from the moment they awaken. As such they hate change, they wish their surroundings to remain as they are and only allow slow and gradual change. Any change too rapid will cause the dryads to intercede, though so long as the change is slow enough they will only rarely do anything, as they understand that life is change and to oppose such is doomed to fail.

Dryads are born from their territory and are bound to it, if they are separated from it for too long or their place of origin were to be destroyed, the dryads would slowly wither and die. Dryads can migrate to a different place of power, but almost never do so unless their home was destroyed.
Their existence is also interlinked, harm to one does harm to the other.
However dryads are exceptionally powerful within their domain, having a great bond to every beast or plant, allowing them to command them and the very land to their advantage.

Nature & Humanity

The places where dryads form are usually far enough from civilisation that they and humanity do not meet.

However when Humanity and nature come into conflict things get ugly. This can happen if humans expand too rapidly into nature and an dryads do not have the time to adapt, or if humanity attacks or offends the dryads. In such situations they will do whatever they think best, and it will not give any considerations to morality or mercy.
The dryads might react to the logging of large swathes of forests by sending swarms of locusts and rats to eat the village's food, driving them to starvation, or destroy their village with landslides and floods.

On the other hand, civilisations can destroy the sacred groves where dryads originate from if angered enough. Entire forests have been burned after a kingdom was spurred to anger, and sacred groves were forever ruined, so the dryads know to avoid angering humanity needlessly.

For this reason, when a sacred grove is found by an explorer or hunter, efforts are made by both side to not step on each-other's toes.

Druids: Dryads are fundamentally a tied to their land and cannot deal very well with problems outside of its domain, or at least not quickly. As the dryads are intelligent and knows this, they are almost always wiling to accept suitable mortals as agents, turning them into druids. They teach them to use the powers of nature in exchange for making them swear oaths to maintain the balance and protect the grove, allowing the druid to also use those powers outside of their lands for their own means.

Appearance:

Dryads are beings resembling walking trees, shrubs and other plants.
When unmoving, they may be indistinguishable from mundane plants.