Iris

Flora & Fauna
The majority of life on Earth, now known as Terra by its inhabitants, has begun adapting in ways to survive a harsher environment in the aftermath of a chaotic change. While many of these changed, some also retained their original life as well, having grown hardier while some split and evolved further to be another subspecies of the original things. Species previously thought to be extinct even have seemingly resurrected themselves from extinction. (Also known as Lazarus species, or Lazarus Taxa/Taxon.) Many species have either evolved further or appear to have de-evolved into what they adapted from in the ancient past.
The climate has changed dramatically, with sea levels having risen, driving the species too weak to adapt into extinction. While the climate has warmed and the Antarctic continent became habitable, the world still faces harsh winters.
(Creator note: All species listed in that link have come back over time.)

Although not an exhaustive list, this lists some examples of major species change over the course of 2500 years.

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FLORA
➤ Trees: Trees of all kinds began to develop harder and sturdier bark and wood, although many old species that survived the war and chaos have remained nearly the same since ancient times, only growing larger.
➤ Carnivorous Plants: Perhaps one of the biggest changes to plantlife, these dangerous plants have grown much larger and attract small to medium sized animals, and will even be able to devour a small human child. Most notably, the spines on some of these plants have become sharper. However, they are also easy to spot, and remain stationary just like their ancestors.
➤ FLORA: (description)
➤ FLORA: (description)

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FAUNA
➤ Birds: Many bird species have split in evolution and grown over time to become massive, terrifying, birds that grew to become fierce hunters during the time where animal life boomed with Humanity's temporary disappearance. Even some prey species became hunters themselves as they found themselves growing large. Various species now obtain some sort of elemental affinity to better protect themselves against the ever-evolving world around them.
➤ Sea Life: Most known sea life remained mostly unchanged outside of populations being restored. Due to how little was already known about it, the greatest change was the emergence of enormous sea serpents, however many whale species have appeared to shrink in size though by how much is dependent on the species. Some species have begun to devolve to what was seen in prehistoric eras.
➤ FAUNA: (description)
➤ FAUNA: (description)