People of Earth are used to the migration of animals. It has become a part of their lives since they first observed and understood that during different seasons, animals would move to different parts of the globe. This has not bothered them, in most cases, it is used as an indicator of the shift in seasons.
But this is not the case for the recent inhabitants of New Terra, the latest in the terraformed planets that humanity has conquered. There are no migration patterns of animals for them to map. The trees migrate.
For millions of years, long before people walked on New Terra, the trees there moved freely. As living entities, they had wills of their own. They had a language with which to communicate with one another. They had their patterns and habits, in almost every respect like a human. Except that when there was a shift in the seasons, the trees would uproot themselves and move.
The idea may seem fanciful or bizarre, but it was a catastrophic event for those settling New Terra. The terraforming took longer to settle than on other planets and moons, primarily because of the great winds that swept over the surface. No matter what they did to conform the atmosphere to that of Earth, the winds would come and destroy whatever work had been done.
We call them winds, but by comparison they were like hurricanes or tornados. The powerful winds would upset the structures that the people had built. Shipments would be greatly delayed because landing pads would be destroyed. People went missing. All the chaos and destruction that they once experienced on Earth was now a norm for the people of New Terra.
In an effort to protect themselves from the terrible winds, people started moving the trees. The idea of transplanting vegetation was an old Earth idea, and trees had been used as a protective barrier against wind for centuries. But the trees of Earth were not the same as the tree of New Terra. These trees did not take kindly to be torn out of their soil and moved to unfamiliar land.
The trees protected. They screamed and yelled at the people mindlessly making this planet their own, but it was all for naught. The tongue of the trees was not one that humanity could understand. For two Earth years, people dug up and transported the trees to a new place. It was at this point that the Christmas War broke out.
It started with the evergreen looking trees. Still full of pine cones, the trees started to launch them towards the settlements of humanity. One would be foolish to think this was in good fun, or that the toss of a pine cone was done playfully. Some 200 people died that day, pine cones lodged deep into their bodies.
Then the trees left, a reverse siege of sorts. They left for other parts of New Terra, leaving humanity to the violent wind and other terrible perils.