Temperate, temperate rain forests cover the surface
The origins of human civilisation upon Cuyavale are unclear. Initial Imperial studies indicate that the world's two populations -- one subterranean and the other arboreal -- both originated at roughly the same time. However, the reasons for their split and continued isolation are lost to time. As there are no known surviving records that predate humanity's activity in the region prior to the Great Crusade in the late 30th Millennium, none are certain when the region might have been first colonised. Adeptus Mechanicus agents might be able to make an estimate after obtaining biological samples, but there are currently no records of anyone conducting such a test.
Humanity first began to colonise Cuyavale in the distant prehistory before the time of the Great Crusade. When remnants of the Angevin Crusade reached the distant world in the 39th Millennium, they were surprised to discover the hallmarks of human life. Further exploration soon revealed two separate populations, which continued to thrive in spite of the world’s deadly predators. After re-establishing contact, the Ecclesiarchy committed missionaries to the world, so that the surviving humans might learn the glory of the Immortal Emperor. While the Imperial Creed now flourishes upon the planet, their physical distance from the remainder of the Calixis Sector has limited the amount of interaction between Cuyavale and the agents of Terra.
The arboreal populations largely dwell within Cuyavale’s enormous trees. These humans seldom descend to the world’s surface, and many spend their entire lives within the boughs of a small grove of trees. Communities are entirely dependent upon the bounty of the tree in which they dwell, and the organisms that live among the enormous plants. While many of these species are able to directly exploit the tree’s biological processes, others merely take advantage of the microclimates that the trees create. These include a broad range of arboreal animals, as well as lesser plants and fungal analogues that have evolved to dwell among the trees. The native humans who live in this environment have domesticated many of these plants for agricultural purposes.
In contrast, the subterranean population lives far beneath the trees, among caves, believed to be the remnants of water flows and root networks that have long since rotted away. These natives are accustomed to lives of perpetual darkness. Their diets are largely based upon fungal growths and the few animals that dwell in the deep shelter of the trees, as they live in perpetual fear of, but relative safety from, the planet's Drakons.
Since the advent of the Severan Dominate, the Secessionist stellar nation has drawn recruits from both of Cuyavale's human populations. Some of these forces have been used in defensive efforts directly upon the planet, as Ork forces have recently begun to assault the world. To date, the Orks have focused much of their efforts on attempts to tame the massive Drakons at the same time as they engage the disparate communities. So far, the xenos have had early success in controlling the Drakons, with at least one beast serving as a sort of aerial transport for the violent Orks.
The world's surface is covered by massive, temperate rain forests. Huge trees, more than a hundred metres in diameter at their bases, extend over a kilometre into the heavens. Closely packed, these enormous plants completely block out the primary’s light from ever reaching the ground. Consequently, those creatures that live among the arboreal heights know a normal day-night cycle, while those that dwell in the shadow of the trees live in perpetual darkness.
While Cuyavale does enjoy some seasonal variation in climate, the massive boles of the world's trees limit these changes. The trees shelter all who dwell at ground level from any prevailing winds in the fall, and provide relief from the sun’s heat in the summer. Few of the enormous trees shed their leaves seasonally. Though there is ample detritus among the shadows of these massive living organisms, little of it comes from the trees themselves. Instead, the animals and lesser plants that live on and among the trees create their own ecosystems, which are often dependent upon the trees.
After considering the trees, the most significant of Cuyavale's life forms are the Drakons. These fearsome apex predators pose a significant threat to any life that travels upon the world. This is, in part, due to the creature's unusual life cycle. Though they can grow to enormous size -- reports indicate mature specimens may have a wingspan in excess of 250 metres -- the flying reptiloids begin life at a far smaller scale. During their mating season, mature female Drakons create nests among the planet’s few arid mountains. These nests are invariably on the borders of the mountainous regions, where they abut with the forests. When the eggs mature and hatch, each nest can unleash thousands of ravenous, metre-long hatchlings upon the unprepared temperate rainforests.
In the weeks that follow, those destructive young often strip hundreds of square kilometres bare as they destroy all life, as well as a significant proportion of their siblings. Only a small percentage of each litter survive this period of frenzied hunting, leaving only the strongest and canniest an opportunity to reach maturity. In the years and decades that follow, the young Drakons continue to grow in size, often preying upon other members of their species at the same time as they devour the world’s other life forms. Explorator survey reports indicate that during the early years of their development, Drakons may grow more than a metre each year, though this rate seems to be largely dependent upon the availability of prey organisms. Because of this, Drakons are fiercely territorial, interacting with other members of their species only during the breeding season. The largest specimens are believed to be many centuries in age, and are fiercely protective of their own domains, savaging anything (be it a lone explorer, an infantry formation, or a main battle tank) that wanders too close to it.
- Only War: Core Rulebook (RPG), pp. 346-348
- Only War: Enemies of the Imperium (RPG), pp. 8-31