Symbolism, Imagery, Allegory
Prince Caspian has an impressive green thumb. It's got everything from talking animals to rivergods, orchards to walking trees, and landscapes as diverse as marshes, forests, seascapes, and rocky gorges.
So you might have found yourself wondering: what's with all this nature imagery? Well, call it tree hugging if you like, but we prefer to call it—
Going Green
Matthew Dickerson and David O'Hara argue that Lewis's fictional works and poetry love to get their environmentalism on. Their reasoning centers on the Lewis's value system as a Christian convert:
One of the most important Christian virtues espoused and illustrated by Lewis […] is the virtue of hospitality. Hospitality stands in direct contrast with exploitation. Hospitality demands that we care for the most vulnerable: the traveler, the stranger, the outcast, the sick, creatures who cannot defend themselves against humans. […] Exploitation, by contrast, takes advantage of that which is vulnerable and powerless. (Source)
If we bring this idea into Prince Caspian, we can see that the creatures unable to defend themselves include the trees, animals, and landscape, while the Telmarines play the role of the exploiters. Caspian and his people then play the role of environmentalists since they not only combat the exploiters in a civil war, but they provide hospitality for the defenseless parts of nature.
In one telling scene, Lucy sees "Coldsley Shovel and his moles scuffing up the turf in various places (which Bacchus had pointed out to them) and realized that the trees were going to eat earth" (15.24). The hospitality of the Old Narnians extends to treating the environment like an honored and cherished guest. They provide and care for nature, and it, in turn, provides and cares for them (by putting a grand whooping on the Telmarines).
The focus on nature comes to symbolize hospitality in general. Be hospitable to others—and even the environment—and it will return in kind. Exploit others and the environment, and well, you'd better keep an extra eye on that tree lurking in your backyard.