The slow war is all around us, but few of us can see it.
Some few druids of Khaldun know about it; those who can cast speak with plants or awaken sometimes come to understand the outer edges of the slow war. The dreaming druids of the Foxfire Forest were vexed (but somewhat sympathetic) when their fellow druid Bardo Urrok announced that the slow war of the wood is too noisy for him, and left their company for less-forested climes. Some travelers have since reported running into the eccentric halfling in the Hoarfrost Ridge, above the timberline.
Those Who Remember awakened a hawthorn bush, and were surprised (and amused) to learn that its morality was totally alien, with a very pragmatic view of murder and a lack of understanding of their own, seemingly-contradictory moral stances. (The bush didn't understand the elf druid's concept of an "invasive species," for example; a creature that outperforms others in an environment is clearly the victor to be lauded rather than lamented.) The bush's exploration of animal-scale life was sadly cut short by a group of dark elves as part of the far-reaching consequences of the Battle of Scandshar.
The key is this: plants are involved in an aeons-long struggle to survive amidst dwindling resources and increasing predation. There is plenty of sunlight and nutrients, but "arbitrarily large" is different than "infinite." They have defenses against herbivores, and are evolving new ones all the time, but herbivores are also adapting at the same glacial pace and move much more quickly. Humans and their ilk choose some plants and inhibit others, seemingly with no rhyme or reason. (And those selfsame creatures will often cultivate land in ways that make it inaccessible to plants of any sort.)
All of this to say that there is a war out there, happening much more slowly than any of us can readily bear witness. This is the slow war of plants. And while plants in folklore and stories are often ancient and placid, depicted as living in harmony with their environment, real plants are bloodthirsty, impatient, and downright Darwinian. They compete for resources, parasitize each other, or even engage in biological warfare. (To say nothing of defenses against herbivores such as poisons and spinose teeth.)
More grist for the mill of common druidic misconceptions.